Lithium Triangle - ARGENTINA - Salar de Olaroz, Salar de Hombre Muerto, Salar de Rincon, Salinas Grande, Sal de Vida, Salar de Cauchari; CHILE - Salar de Atacama; BOLIVIA - Salar Uyuni
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This record provides an overview of the 'Lithium Tiangle' which covers sections of NW Argentina, northern Chile and Bolivia, and is estimated to contain at least 75% of the world's lithium resources as known in 2015. It provides brief summaries of a selection of the key lithium salars across the triangle in all three countries, as well as details of other salars that do not currently host defined resources.
The second part of the record describes in detail the regional setting, geology and mineralisation of one of the key deposits within the 'triangle', the Salar de Olaroz lithium carbonate brine extraction operation which is located ~160 km NW of San Salvador de Jujuy, at an altitude of 3900 m asl in the elevated and arid Puna region of Argentina's north-west province of Jujuy (#Location: 23° 29' 34"S, 67° 42' 26"W).
Lithium Triangle Deposits
The key operations and undeveloped resources of the Lithium Triangle, which occur within similar settings to the Salar de Olaroz described in more detail below, include:
• Salar de Atacama on the western margin of the Andean Altiplano in northern Chile, ~210 km east of Antofagasta. It is operated by Sociedad Quimica y Minera de Chile S.A. (SQM), producing lithium carbonate, potassium chloride, potassium sulphate, boric acid and magnesium chloride. At 3000 km2, it is the largest salar in Chile, containing 7.5 Mt, or 27% of the world's lithium reserve base as known in 2015. In 2015, the operation produced 12 900tonnes of contained lithium. The brine contains mean concentrations of 1835 mg/L Li; 22 626 mg/L K; 11 741 mg/L Mg; 379 mg/L Ca; and 783 mg/L B; with moderate Mg:Li ratios of ≥4. At the operation site, the annual evaporation rate averages 3500 mm per annum, and has a low annual rainfall of only a few mm per year.
• Salar Uyuni, in Bolivia, is the largest salt lake in the Andes, covering an area of 10 582 km2, located within the Bolivian Altiplano, at an average elevation of 3700 m. Reserves are estimated at ~9.0 Mt of Lithium, from brines containing up to ~3000 mg/L Li. Mean brine grades are 424 mg/L Li and 8719 mg/L K, 7872 mg/L Mg, 557 mg/L Ca and 242 mg/L B. The brine is a saturated solution of sodium chloride, lithium chloride and magnesium chloride in water. However, compared to the Salar de Atacama, the Salar Uyuni has a higher rainfall, and a cooler climate, resulting in an evaporation rate less than half of that at Salar de Atacama. In addition, the high magnesium chloride content (Mg:Li ratio of >14) must be removed through an expensive chemical process.
• Salar de Hombre Muerto, in NW Argentina, is located in NE Catamarca Province, 720 km NNW of the capital, San Fernando del Valle de Catamarca, and ~1400 km northwest of Buenos Aires. It is situated in the southern Puna de Atacama of the high Andes at ~4000 m above sea level. The Puna is a plateau composed of basins and ranges, discrete from the much larger Cordillera-bounded Altiplano basin to the north. The area receives just enough rainfall to occasionally be covered by a thin layer of water. The lithium brine extraction and processing facility is operated by FMC Lithium, through its subsidiary Minera del Altiplano S.A. The brines contain 744 mg/L Li and 7404 mg/L K, 1020 mg/L Mg, 636 mg/L Ca and 420 mg/L B, although only lithium is extracted. The lithium salts produced on site are transported 99 km by road to the Salar de Pocitos station of the railway line that links through Chile to the port of Antofagasta on the Pacific coast. Most of Argentina's production of 3800 t of Li in 2015 was from Salar de Hombre Muerto. The operation has been producing lithium since 1997 and according to FMC Lithium has a mine life of >75 years.
• Salar de Rincon, in NW Argentina, is located in the NW corner of Salta Province, close to the Chilean border, ~ 180 km NW of the provincial capital Salta, and 145 km north of the Salar de Hombre Muerto. The resource was explored and tested by Rincon Lithium Limited, a subsidiary of Admiralty Resources NL, but has subsequently been acquired by the Sentient Group. In 2007, Rincon Lithium announced JORC compliant estimated proved plus probable reserves of 1.4 Mt of lithium (~7.3 Mt of lithium carbonate) and 50.8 Mt of potash. The brine contains mean concentrations of 397 mg/L Li; 7513 mg/L K; 3419 mg/L Mg; 494 mg/L Ca; and 331 mg/L B.
• Salinas Grande, in Jujuy Province, NW Argentina, ~65 km ESE of Salar de Olaroz and ~90 km NW of San Salvador de Jujuy. It occurs in an ~ENE trending salar in the eastern Puna. In March 2012, Orocobre Limited announced the initial resource estimate of 56.5 Mm3 of brine @ 795 mg/L Li and 9550 mg/L K, which is equivalent to 0.2392 Mt of Li2CO3 and 1.03 million tonnes of KCl. The estimate extends to an average depth of 13.3 m.
• Sal de Vida, in NW Argentina, is located at an altitude of 4025 m, covering 385 km2 of the eastern half of the Salar de Hombre Muerto in NE Catamarca Province, ~10 km to the ENE of the FMC Lithium operation. In 2013, Galaxy Resources Limited reported a JORC compliant total mineral resource on their website (visited, June 2016) of 1810 Mm3 (including 830 Mm3 inferred resources) of brine @ 753 mg/L Li, 8377 mg/L K; and a Maiden Reserve estimate of 1.14 Mt of retrievable Li2CO3 equivalent (0.214 Mt of Li) and 4.2 Mt of KCI (2.2 Mt of K). Reserve and resource estimates are based on a 500 mg/L Li cut-off. The brines have low magnesium (Mg:Li ratio ~2.2) and sulphate (SO4:Li ratio of 11.5). In addition to the brines, the Salar hosts near surface deposits of the boron mineral ulexite [NaCaB5O9•nH2O - n=8 or 5].
• Salar de Cauchari, in Jujuy, NW Argentina, is located immediately to the south of Salar de Olaroz, and is a narrower continuation of the same basin. Mean brine grades are 618 mg/L Li and 5127 mg/L K, 1770 mg/L Mg, 401 mg/L Ca and 1360 mg/L B. Published NI 43-101 compliant measured + indicated mineral resource over an area of ~26 x 4 km in two blocks, one in the Salar de Cauchari and the other on the eastern side of the Salar de Olaroz were a combined total of 1.0 Mt of Li metal in brine @ 656 and 637 mg/L Li respectively, and 9.0 Mt of K metal in brine @ 5900 and 5700 mg/L K respectively (NI 43-101 Technical Report, Lithium Americas Corporations, February 2010).
Brine grades quoted for Salars de Atacama, Hombre Muerto, Rincón and Uyuni from "Pavlovic, P. and Fowler, J., 2004 - Evaluation of The Potential of Salar del Rincon Brine Deposit as a Source of Lithium, Potash, Boron and other Mineral Resources".
The following summaries and analyses are from a regional reconnaissance of the salars of the Argentine Puna reported by López Steinmetz (2020) and do not imply the presence or absence of economic accumulations of lithium.
• Salar de Centenario is a 7 km2 playa lake located at an altitude of 3816 m a.s.l., surrounded by 70 km2 of saline muddy shore zones. Brines from the salar are alkaline, with pH values of between 7.50 and 7.70, and TDS (Total Dissolved Salts) ranging from 26 090 to 48 590 mg/L. Li+ concentrations range from 25 to 377 mg/L, with a mean of 141 mg/L. Boron concentrations range between 277 and 581 mg/L, and the mean Li/B ratio is 0.97.
• Salar de Diablillos is a 4 km2 playa lake located at an altitude of 4032 m a.s.l., surrounded by 29 km2 of saline muddy shore zones. The brines are alkaline with a pH of 8.00 and TDS values ranging between 26 350 and 80 735 mg/L. Li+ concentrations vary from 47 to 357 mg/L, with a mean of 180 mg/L. The mean Li/K ratio is 0.26, and the mean Li/Mg = 0.26. Boron concentrations are up to 808 mg/L, with a mean Li/B ratio of 0.86.
• Salar de Pastos Grandes is a 27 km2 triangular salt pan, with an adjacent 4.8 km2 saline lake, located at an altitude of 3780 m a.s.l. The brines are alkaline with a pH between 8.00 and 8.30, and TDS values ranging between 154 030 and 226 600 mg/L. Li+ concentrations vary from 305 to 857 mg/L, with a mean of 483 mg/L. The mean Li/K ratio is 0.82, and the mean Li/Mg = 0.19. Boron concentrations are from 300 to 812 mg/L, with a mean Li/B ratio of 2.24.
• Salar de Pozuelos is a 75 km2 oval shaped salt pan, located at an altitude of 3663 m a.s.l. The brines are alkaline with a pH between 7.80 and 8.60, and TDS values ranging between 205 243 and 298 574 mg/L. Li+ concentrations vary from 75 to 940 mg/L, with a mean of 401 mg/L. The mean Li/K ratio is 0.69, and the mean Li/Mg = 0.43. Boron concentrations are from 202 to 2102 mg/L, with a mean Li/B ratio of 1.26.
• Salar de Ratones is a north-south elongated, 3 km2 playa lake located at an altitude of 3822 m a.s.l., surrounded by 47 km2 of saline muddy shore zones. The brines are alkaline and moderately saline with TDS values ranging between 28 080 and 82 580 mg/L. Li+ concentrations vary from 88 to 260 mg/L, with a mean of 158 mg/L. The mean Li/K ratio is 0.38, and the mean Li/Mg = 1.24. Boron concentrations are from 312 to 509 mg/L, with a mean Li/B ratio of 1.06.
• Salar de Antofalla-Botijuelas is a north-south elongated, up to 100 km long salar covering an area of 655 km2 located at an altitude of 3330 m a.s.l. There are abundant thermal
springs in this salar, especially on the northern and central-western margins. The brines are only slightly alkaline with pH values between 7.40 and 7.80, and moderately saline with TDS values ranging between 9 110 and 184 570 mg/L. Li+ concentrations increase northwards from 46 to 615 mg/L, with a mean of 209 mg/L. The mean Li/K ratio is 0.90, and the mean Li/Mg = 0.64. Boron concentrations are from 415 to 878 mg/L, with a mean Li/B ratio of 0.83.
• Salar de Arizaro is the largest salar in the Puna plateau in Argentina, covering an area of 1708 km2 located at an altitude of 3474 m a.s.l. The brines are only slightly alkaline with pH values between 7.30 and 7.40, with TDS values ranging between 38 865 and 308 175 mg/L. Li+ concentration varies from 52 to 465 mg/L, with an increase toward the south-central part of the salar, and a mean of 191 mg/L. The mean Li/K ratio is 0.24, and the mean Li/Mg = 0.16. Boron concentrations are from 380 to 3382 mg/L, with a mean Li/B ratio of 0.28.
• Salar de Pocitos-Quirón is a north-south elongated composite saline system, comprising the 28 km2 Pocitos salt pan zone and the 422 km2 Quirón playa lake, located at an altitude of 3663 m a.s.l. The brines are alkaline with a pH between 7.80 and 8.30, and TDS values ranging between 29 480 and 299 217 mg/L. Li+ concentrations vary from 22 to 101 mg/L, with a mean of 57 mg/L. The highest grade zone in the central part of the Pocitos salt pan. The mean Li/K ratio is 0.26, and the mean Li/Mg = 0.17. Boron concentrations are from 60 to 208 mg/L, with a mean Li/B ratio of 1.37.
• Salar de Río Grande is an elliptical salar system covering an area of 176 km2 located at an altitude of 3668 m a.s.l. The surface of the salt pan zone covers
56 km2, with the remaining section of the salar comprising a 120 km2 saline muddy playa lake that extends to the south. The brines are neutral to slightly alkaline with pH values between 7.00 and 7.20, and TDS values ranging between 199 070 and 284 605 mg/L. Li+ concentration varies from 139 to 692 mg/L, with a mean of 396 mg/L, with the highest Li grade measured in the central part of the salar. The mean Li/K ratio is 0.72, and the mean Li/Mg = 0.33. Boron concentrations are from 303 to 545 mg/L, with a mean Li/B ratio of 2.81.
The Andean orogenic belt have been developed on an active plate margin since Mariana-style subduction of the Farallon plate commenced along the west coast of South America during the Early Jurassic (195 to 130 Ma). Subduction was initially expressed by an intra-oceanic island arc, before moving eastward to form a continental arc during the mid Cretaceous (125 to 90 Ma). An extensional regime persisted through the late Cretaceous, generating back-arc rifting and grabens (Salfity and Marquillas, 1994). Marine sediments from this period, covering most of the Central Andean region, indicate an extensive back-arc seaway with little land above sea level (Lamb et al., 1997; Scotese, 2001).
These rocks, and the succession below, were deposited over a basement of Meso- to Neoproterozoic terranes accreted to the Archaean to Proterozoic shield to the east, overlain by Ordovician to Carboniferous marine and lesser volcanic rocks that formed the western margin of South America in the Mesozoic.
Late Cretaceous to late Eocene (78 to 37 Ma) - Over this period the arc migrated further east to the current Chilean Precordillera, the Cordillera de Domeyko of northern Chile, while extension continued in the back-arc to the east (Allmendinger et al., 1997; Lamb et al., 1997). Significant shortening commenced during the 44 to 37 Ma Incaic Phase, largely in the west, with associated uplift to perhaps 1000 m (Gregory-Wodzicki, 2000) creating a major north-south watershed. Coarse clastic continental sediments eroded from this ridge indicate eastward transport in Chile and Argentina (Jordan and Alonso, 1987). The subsequent initiation of shortening and uplift of the Eastern Cordillera of Argentina at ~38 Ma, led to the development of a second north-south watershed with coarse continental sediment accumulating between the two ranges throughout the Puna in northern Argentina and Altiplano in northern Chile and Bolivia (Allmendinger et al., 1997; Coutand et al., 2001).
Late Oligocene to early Miocene (25 to 20 Ma) - The volcanic arc migrated marginally eastward to the Western Cordillera. At the same time, significant shortening across the Puna and southern Altiplano to the east, and associated reverse faulting led to differential uplift of adjacent fault wedges, initiating a basin and range terrane with separate fault bounded depocenters. Major uplift of the Altiplano-Puna plateau began during the middle to late Miocene (15 to 10 Ma), perhaps reaching 2500 m by 10 Ma, and 3500 m by 6 Ma (Garzione et al., 2006). Coutand et al. (2001) interpret the reverse faults as being responsible for increasing the accommodation space in the basins by uplift of mountain ranges marginal to the Puna salar basins. Subhorizontal east-west shortening, thickening and uplift, was achieved by the development of an east vergent mid-crustal decollement, above which, east vergent thrusts to the west and west vergent thrusts to the east, imbricated the basement to create ranges bordering the salars in the centre. Paleogene to Neogene deposits accumulated in the salar basins framed, and overlain by uplifted and thrusted Ordovician to Cretaceous bedrock.
To the west of Salar de Olaroz, the north-south striking reverse faults that cut lower to middle Miocene strata are covered by 9.5 Ma continental clastic and pyroclastic strata (Marreti et al., 1994; Schwab and Lippolt, 1976; Schwab, 1980). On the west the flank of the Salars de Olaroz-Cauchari, Ordovician sedimentary rocks are found overthrusting late Miocene sedimentary rocks (Kay et al., 2008).
The 10 to 5 Ma late Miocene volcanic event, centered on the Altiplano-Puna Volcanic Complex between 21 and 24°S (de Silva, 1989), produced significant caldera subsidence and associated extensive ignimbrite sheets, as well as andesitic-dacitic stratovolcanoes. In the Puna, volcanic activity was constrained by numerous major NW-SE crustal megafractures (Chernicoff et al., 2002), that are evident along lineaments to the south of the Salar de Olaroz (Salfity, 1985).
Early to middle Miocene, red bed sedimentation occurs throughout the Puna, Altiplano and Chilean Pre-Andean Depression (Jordan and Alonso, 1987). Intensification of thrust faulting, uplift and volcanism during the middle to late Miocene, produced isolated, internal drainage fed, sedimentary basins separated by mountain ranges, bounded in turn, by the major watersheds of the Cordilleras to the west and east of the Puna. Sedimentation in these basins began with alluvial fans being shed from the uplifted ranges and continued to form playa, sandflat and mudflat facies.
The Puna of northern Argentina, and the Altiplano of eastern Chile and Bolivia have had a semi-arid to arid climate since at least 150 Ma. This has been a result of the regions stable location relative to the 'Hadley circulation' (tropical atmospheric circulation cell between the equator and the sub-tropics that produces the 'SE Trade winds'; Hartley et al., 2005), combined with the uplift of the Eastern Cordillera blocking all flow of moisture, leading to increased aridity since at least 15 to 10 Ma. The high radiation and evaporation levels, and the low precipitation rates has resulted in increased aridity in the Puna, which, combined with the internal drainage, has led to the deposition of evaporite precipitates in many of the Puna basins.
Pliocene to Pleistocene - During this period, contractional deformation migrated eastward out of the Puna into the Santa Barbara system, coeval with major global climate changes (e.g., the ice ages) leading to a fluctuating regime of short periods of alternating wetter and drier conditions. As a consequence of both frequent periods of aridity and a reduction in erosion and accommodation space due to greater tectonic stability, the sediment accumulation in the isolated basins was limited. Nevertheless, continuing runoff on both the surface and underground, continued solute dissolution from the basins and concentration in their centres where evaporation is the only escape.
Evaporite minerals are found as both disseminations within the host clastic sequence and as discrete beds. The earliest evaporite formation was in the middle Miocene, with an increase in both frequency and magnitude tends during the Pliocene to Quaternary (Alonso et al., 1991; Vandervoort et al., 1995; Kraemer et al., 1999). Dating of the similar thick halite sequences in the Salars de Hombre Muerto (220 km to the south in Argetina) and Atacama (Chile) suggest that they have mostly formed after 100 Ka (Lowenstein, 2000; Lowenstein et al., 2001).
Salar de Olaroz
The stratigraphic succession in the Salar de Olaroz area (after Houston and Gunn, 2011) is as follows, from the base:
Ordovician - a marine, marine delta and volcanic sequence of sandtones, mudstones and limey units, volcaniclastic sediments and turbidites;
Unconformity above folded Ordovian rocks;
Post-Ordovician Palaeozoic intrusions porphyritic and equigranular granitoids which are calc-alkaline and have dacitic to rhyolitic compositions;
Silurian to Carboniferous - largely composed of marine platform and turbidite deposits of sandstones, conglomeratic sandstones, siltsones and diamictites. These rocks have been subjected to isoclinal folding, with NW-SE trending axes;
Cretaceous - commencing with early Cretaceous granites, syenites, monzogranites and granodiorites;
- Continental sedimentary rocks - Red alluvial and fluvial sandstones, silty claystones and conglomerates;
- Commencement of the Peruvian orogenic phase - extension and deposition of marine sedimentary rocks;
- Continental and marine sedimentary rocks - calcareous sandstones and continental/marine sandstones, limestones and mudstones;
• Paleocene to Mid Eocene
- continuation of the continental and marine sedimentary sequence from the Cretaceous, with the upper section of continental to marine calcareous sandstones in the Paleocene, overlain by
- lower to mid Eocene fluvial and aeolian alternating conglomerates and red sandstones, limy sandstones, siltstones and claystones;
• Incaic Phase II compression, thrusting and folding;
• Upper Eocene and Oligocene
- Continental red bed sequences - Alternating coarse conglomerates, red sandstones, siltstones and claystones, overlain by red aeolian sandstones;
• Miocene - comprising a sequence as follows:
- Continental sedimentary rocks - Sandstones and interbedded claystones, overlain by sandstones and conglomerates, with tuffs and ignimbrites;
- Rhyolitic and dacitic volcanic complexes, with interbedded continental sediments - including andesite to dacite lavas, domes and ignimbrites and the ~10 Ma Susques Ignimbrite;
- Dacite domes, pyroclastics and subvolcanic intrusives, including the Yungara dacite domes;
- End of 15 to 9 Ma Quechua Phase II compression, and associated folding, and WNW-ESE thrusting from 13 to 4 M;
- Continental sedimentary rocks interbedded with andesitic and dacitic, lavas, volcanic breccias, tuffs, and ignimbrites - one tuff dated at ~10 to 7 Ma;
- Continental sandstones, mudstones and tuffs dated at ~7 to 6.5 Ma;
- Dacitic ignimbrites;
- Andesitic to dacitic volcanic complexes interbedded with continental sedimentary rocks, part of a major period of caldera collapse and volcanic eruption from 8 to 6 Ma;
• Pliocene - Continental sandstone, conglomerate ±mudstone with variable andesite, dacite lavas and ignimbrites;
- Alluvial, colluvial, glacial and lacustrine sediments in closed basins and fan deposits, and ignimbrites erupted from volcanic centres. During this period there was NE-SW directed shortening from 0.2 Ma due to strike-slip faulting;
• Holocene - Salar and lacustine deposits in closed basins, with peripheral colluvial and alluvial sediments, with continued post-Quechua deformation.
The Post Miocene Olaroz basin and the contiguous Cauchari basin immediately to the south, are bounded by an inwardly vergent pair of north-south striking thrust faults, which can be seen to thrust Ordovician and Cretaceous basement rocks over the Cenozoic basin fill (Kay et al., 2008). The Cenozoic basin infill is ~800 to 1200 m deep, based on gravity data. Geophysical data also suggests that inward from and below the basin boundary thrust faults, a series of north-south normal faults downthrow towards the basin centre along both its east and west sides.
The basin is infilled with Cenozoic sediments, with Pliocene to Recent sediments forming a multilayered aquifer that is present to depths of 200 m, and probably significantly deeper, that acts as a host to a brine containing elevated levels of dissolved lithium, potassium and boron.
Within the basin, outcrop along both the east and west sides comprises an outer Paleogene suite and inner Neogene sediments, which gravity data suggests also underlie the central post-Miocene sedimentary rocks.
North-south aligned outcrops of the Miocene Yungara dacite and a Pleistocene olivine basalt occur along the SE side of the Olaroz basin, suggesting intrusion along hidden normal faults. The oldest basin unit, beyond the margins of the salar deposits is composed of Plio-Pleistocene sheet sands and coarse talus gravels eroded from the bounding ranges. The salar margins comprise finer grained sands and silts with abundant disseminated and interbedded calcite and gypsum, considered to be playa facies.
Marginal alluvial fans and fan delta - a fan-delta and three alluvial fans enter the salar in the north and SW, and interdigitate with the salar sediments at depth. The Rosario fan-delta, to the north of the salar, covers an area of 60 km2 at the surface, has a lower gradient and is more extensive than the alluvial fans, although gravity data indicates it may be even more extensive at depth. It is is sourced from a 2000 km2 catchment to the north.
Typically, the fan delta interfingers with the salar basin fill units, e.g., in one drill hole over a 54 m vertical interval, the upper 20 m of fan delta sediments intertongue with 3 to 4 m of basin Unit B (see below) in the upper 10 m, and 2 m of Unit C at 20 m depth. Over this interval, the fan delta deposits largely comprise beds of coarse sand to gravel (1 to 7 cm), alternating with some beds of fine sand and occasional beds up to 1 m thick of silty clay and clay. Thin beds (<1 m) of palaeosol carbonates occur at three levels, as calcretes. From 20 to 54 m, up to 3 m thick beds of fine to medium grained sands alternate with silty sand and clay horizons that are up to 1 m thick. The sands and gravels comprise <95% subangular quartz, 2 to <50% metamorphic and volcanic lithic fragments, <10% magnetite, <4% biotite, <4% calcite, <3% gypsum and , <10% clay, reflecting lithologies in the catchment. Bedding is massive, or layered with laminations of finer grained material. Interbed erosional surfaces are present as are rare grading and cross lamination. The occurrence of these sediments suggest a distributory fluvial system or braided delta (Stanstreet and McCarthy, 1993; Miall, 1996), where deposition has been largely subaerial), but also at times subaqueous.
The Archibarca alluvial fan, the largest and most active of the three that enter the salar, has been derived from a 1200 km2 catchment to the west. Over a 52 m vertical interval an upper unit is dominated by gravel and fine sand, and a lower Unit is largely sandy gravel. All three alluvial fans are dominated by debris flow and planar sheetflood couplets of gravel/sand or gravel/clay, with couplets ranging from cm to m scales. The gravel beds are composed of ~10 cm subrounded clasts at the fan apex, but decreasing down fan. The gravel beds are either clast or matrix supported with some crude, thick cross-stratification and occasional grading. These sheetflood deposits have wide, belt-like geometries which can be traced over many hundreds of meters and are cut by occasional shallow, erosive based, gravel filled, avulsion channels.
Basin succession in the Salar Nucleus
Within the basin, the aquifer may be subdivided into 8 units that can be correlated throughout the basin. These units are composed of coarse to fine-grained sands, silts and clays, with varying amounts of evaporitic halite and ulexite, as well as calcite as calcrete or travertine. Evaporitic beds dominate the basal and upper units of the nucleus of the basin. To the north and south, these units interdigitate with coarse sediments of the Rio Rosario fan-delta and the Archibarca alluvial fan respectively, although the latter has only been active during the deposition of the upper four units.
Each unit is thin-bedded, with individual beds that are from a few mm to a few tens of cm thick, although individual beds can not be followed for more than a few metres. These beds rapidly alternate in colour, appearance or grain size along strike. In addition, the grain size of any particular bed is generally not uniform and may comprise silt to clay size particles with some sand mixed in, and hence references to a sand dominant or clay dominant bed, it is taken to refer to the bulk composition.
Testing of the deposit involved two stages of drilling, the first in which all holes were drilled to 54 m depth. Based on the lithological and geophysical logs from these holes, four lithostratigraphic units, A to D inclusive, were assigned, although the base of Unit D was not intersected in this program. A second phase of more widely spaced holes, cored from 54 to an average depth of 197 m was then undertaken and Units E to G inclusive defined.
• Salar Crust - the nucleus of the salar basin is covered by a superficial halite crust that has been subdivided into:
i). Old crust, occurring as low (<0.5 m) rugose pinnacles of halite that are greater than 10 years old (based on the age of similar structures at the salars de Atacama and de Hombre Muerto).
ii). Recent, 2 to 5 years old, halite crust, occurring as halite with well-developed contraction polygons.
ii). Re-solution crust, which is smooth, with high reflectance, usually found along the side of the nucleus, which has recently (<2 years) undergone inundation by precipitation or flooding, and subsequent been re-precipitated as halite.
• Unit A - which has been found in all test wells, except where it is replaced by the Archibarca marginal alluvial fan and Rosario fan delta facies in the south and north respectively. It has a maximum thickness of 18 m, but thins and pinches out on all margins, forming a shallow basin with the main depocenter in the central southern part of the salar. It is dominated by >80% halite in the NW and 50% in the SW, with an increasing sand fraction to the SE (to 15%), and clay fraction to the NE (to 98%). Rare, <20 cm thick beds of ulexite and gypsum are found towards the NE, associated with the clays. The halite may be coarsely or finely crystalline and relatively pure, or mixed with clay, which is commonly black and organic. The sand is generally fine grained with considerable silt and some clay. The latter are red-brown, green or dark and organic rich. The unit has considerable lamination and thin bedding. On the basis of the lithology and structures, it is interpreted to represent alternating subaqueous (coarse halite crystals forming on lagoon floors and organic rich shallow lagoons to marshes) to subaerial (fine halite crystals indicate surficial evaporation and precipitation) deposition, with periodic flooding (sand) from the south.
• Unit B - that is found everywhere except where it is replaced by the Archibarca marginal alluvial fan and Rosario fan delta facies in the south and north respectively. It has two thicker accumulations with maxima of 36.2 m and 28 m in the north central and south central sections of the basin, separated by the thinnest development, where it is only 11.5 m thick, but is mostly >20 m. It rapidly thins to zero, or possibly finely interdigitates, with the marginal alluvial fan and fan delta facies.
Unit B of composed of interbedded sediments, dominated by generally >75% clay over the whole area, with a sand fraction locally reaching 30% in the NE, and halite reaching 18% in the central east. The clays are plastic, red-brown, green or black and organic rich. They have convolute lamination and load structures with discontinuities, and are frequently laminated and silty with thin sand lenses, containing widely disseminated crystals of selenite. Rare nodules of ulexite are found, whilst there are also a few occurrences of either cinnabar (HgS) or realgar (AsS). In the NE, the sand is usually fine grained and silty. Halite is fine grained and mixed with silt and clay. It is interpreted to have been deposited in an eutrophic (i.e., excessively nutrient rich), strongly reducing lake, with some periodic flooding from the NE, associated a the large fan-delta, where halite precipitated in its distal limits. The soft sediment structures imply the unit was originally deposited with loose packing-high porosity, and is undergoing internal deformation by sediment gravitational reorganisation (Raleigh-Taylor instability). As such it may currently be considered underconsolidated. The selenite and ulexite displace surrounding clays, consistent with post-depositional, diagenetic growth in situ occurring when connate water is ejected during compaction. The sulphide minerals are suggested to indicate a nearby geothermal source.
• Unit C - is a well defined sand bed, occurring throughout the salar and interdigitating with the Archibarca marginal alluvial fan and Rosario fan delta facies in the south and north respectively. It ranges from 6.6 to 0.1 m in thickness, tending to be thicker in the north and south and thinner in the core of the salar. It does not contain any halite. The sand fraction averages 80% but reaches 100%, except for one anomalously low of 6% in the central east part of the basin. The sand is universally underlain by clays or silty clays of Unit D. The sand is fine to medium grained, well sorted, and dominated by quartz, but with some biotite. In section of the northern part of the basin, a <50 cm thick horizon is well cemented with calcite. The origin of this unit is unclear.
• Unit D - the lowermost of the units defined in the first program of drilling. This unit is replaced by the sediments of the Rosario fan delta facies in the north respectively. The Archibarca marginal alluvial fan is not represented in the sequence from slightly below the base of Unit C. The base of Unit D was not intersected in these drill holes and hence the unit may be thicker than described. The thickness of the unit, as intersected, increases from ~20 m in the central east to over 32 m in the west and NW.
A normal faults on the western side of the basin, appears to have been a growth fault during deposition of the units D to G respectively. It shows a significant downthrow to the west in the south, but rotates to downthrow slightly to the east in the north, influencing the thickness of these units.
Unit D comprises interbedded sediments comprising >60% clay and silty clay, with lesser fractions of sand and thin beds of carbonate (calcrete or travertine), as well as rare lenses of halite and ulexite (<0.5 m thick) towards the south.
The clays are generally red-brown or green, and only rarely black and organic rich. They are frequently silty, with thin fine to coarse grained sand fraction beds between 10 cm to 3 m thick. Correlation of these sand fraction beds between drill holes has not been possible so their continuity is unknown. Material described as sandy clay is recorded as containing significant quantities of pore fluid. Whilst the clays and the carbonates may indicate prevailing lacustrine conditions, it appears to be less eutrophic compared to Unit B, and frequent mixed size sand intercalation suggests receipt of periodic fluvial influxes and better aeration of the lake.
• Unit E - the first encountered in the second, deeper phase of drilling below 54 m depth. This unit has a general increase in thickness from <10 m in the south to >30 m in the north. It is dominantly a clay rich sediment, frequently with silty laminae, in the south, center and east, whilst minor sand is encountered in the northern half of the salar, originating or associated with the Rosario fan-delta. Carbonate facies, as calcrete or travertine, constitute up to 50% of the thickness in the NW quadrant of the salar, whilst thin beds of halite are found throughout the west, into the center of the salar.
Clays are red, brown or green, and are sometimes black with entrained organic matter. They are frequently interbedded with silts, sands and even gravel in the northwest. Carbonates occur as discrete, up to 10 m thick beds, composed of crystalline calcite with an overgrowth of calcite cement. Druses with microcrystalline calcite interiors are occasionally found, containing some clastic material as lithic and thin silts beds.
The lithofacies suggest mixed fluvio-palustrine and lacustrine conditions, with the former prevalent to the north and west, the latter towards the south and east, suggesting a northward provenance for the sediments, and a probable connection through to the Salar de Cauchari in the south. There is little or no evidence that the Archibarca and other marginal alluvial fans were active at this stage.
• Unit F - which is relatively thick, increasing from <20 m in the south to 90 m in the north. Overall it is clay dominated, although frequent thin sand beds occur throughout much of the eastern part of the salar, becoming more prevalent in the west. Throughout the western section of the salar, thin ulexite, halite and carbonate beds occur. Based on structural observations and distribution of lithofacies, active subsidence appears to have taken place on the western margin of the basin, where deeper water lacustrine conditions prevailed, whilst it is likely that tilting of the whole basin towards the north was also occurring at the same time.
• Unit G - was not fully intersected by any of the deep drill holes, which were terminated on average at 297 m, and consequently no reliable thickness estimates are available. Geophysical data suggests the base may be as deep as 600 m. As with the overlying unit, clays dominate the far eastern side of the basin, with considerable sand in the west. The clays are red, brown, grey and green with widespread, but uncommon, nodules of ulexite. The sand is generally fine to medium grained with some silt. Halite is found in this unit throughout the salar, but in the NW it occurs as a single, 25 m thick bed, which separates into a number of discrete beds elsewhere in the basin. The west to east asymmetry of the lithofacies suggests active subsidence in the west, probably on the identified normal fault in this area. The distribution of halite also suggests active subsidence in the west and north, and that the discrete halite beds are a function of tectonics rather than changing climatic conditions. The near 100% halite fraction in the northwest does however suggest more stable arid climate conditions than at any other time in the sequence.
Basin Development- The Salar de Olaroz originated as a fault bounded, closed basin during the late Paleogene to Early Neogene, which subsequently during much of the Miocene, appears to have been slowly filled by coarse to medium grained talus slope and alluvial fan deposits eroded from the adjacent mountain ranges. As the basin was filled the detritus became progressively finer grained, deposited in braid-plain, sand-flat, playa and fluvial regimes as observed in the Upper Miocene and Pliocene. A progressively more arid climate during the Pliocene led to the first appearance of evaporitic deposits. Normal faulting probably produced additional subsidence during this time.
The oldest drilled sections, i.e., Unit G, indicate an arid climate with abundant halite, which are probably Pleistocene in age, and likely contiguous with the lowest drilled and reported sediments in the Salar de Cauchari to the south, suggesting the two basins were a continuous hydrologic entity at that stage. Succeeding Units imply continued subsidence in the basin centre, with a climate that was variable, but never as arid as during deposition of Unit G. The subsidence rate decreased through Units E and F and effectively stopped during Unit D. Until that stage, the dominant source of detritus appears to have been from the Rosario catchment to the north. Early during Unit D deposition, a breach in the mountain range to the west allowed sediment to be supplied to the southwestern part of the salar from the Archibarca catchment.
Three major depositional cycles are interpreted to have occurred, presumably in what is largely the Pleistocene to Holcocene: i). Unit D, which represents shallow, largely freshwater conditions in the salar, interfingering with associated alluvial fan and fan-delta deposits the south and north of the salar respectively. This cycle is separated from the next by a widespread, relatively thin Unit C, taken to represent a short but significant interval of wetter conditions; ii). Units B and laterally equivalent alluvial fan and fan-delta deposits, which suggest eutrophic, lacustrine conditions in the salar possibly with some volcanic or hydrothermal supply; and iii). Unit A, which suggests a return to relatively arid conditions with infill largely confined to the basin centre.
Aquifers and Aquitards
Aquifers and Aquitards - The sequence within the salar basin as described above, represent a multi-aquifer system. Based on lithology, Units A, C and G would be the most permeable, whilst Units B, D, E and F would be less permeable. However, the rapid alternation of beds and laminae within each unit, suggests that on a large scale (hundreds of metres to kilometres) the sequence is relatively homogeneous and isotropic, supported by pumping tests that show no evidence of semi-confined conditions nor of significant anisotropy. In addition, head data from drilling suggests the units are in hydraulic contact with each other. On the smaller metre scale, some inhomogeneity and anisotropy is evident, with thin discontinuous confining beds apparent, but it is unlikely this will have any significant influence on the flow of fluid throughout the system.
Porosity is dependent upon lithology, and as the lithologies are highly variable, with sand-silt-clay mixes spanning the full spectrum of possibilities, it is only possible to discriminate the dominant lithology. Consequently, the porosity of sand dominant, or clay dominant lithologies occupy a wide range with considerable overlap, with decreasing porosities and increasing specific yield (the quantity of water which a unit volume of aquifer, after being saturated, will yield by gravity), in the following order - clay dominant → Silt & sand-clay mixes → sand dominant → halite dominant. Porosity distribution in each Unit reflects the dominant lithology across the unit. Over the 200 m depth range tested by drilling, there is also no significant depth-porosity relationship due to the lithology control.
Permeability - Pumping tests show consistent values of permeability for the sediments, with higher rates of 1 to 2 metres/day in fine grained sand aquifers and lower ~0.15 m/d in silts.
The brine body is reasonably homogeneous, extending throughout the salar nucleus at the surface, but expanding considerably with depth in the north where it is unconstrained in the sediments of the Rosario fan-delta and similarly to the south in the Archibarca marginal alluvial fan. To the east and west, the margins are much steeper and more abrupt, probably as a result of reduced permeability in the silt and clay rich eastern and western margins and faulted basin margins, inhibiting movement.
The chemistry of the brine suggests that it was formed by the evaporation of inflowing dilute waters of only one type that initially saturate in and precipitate calcite, followed by gypsum. Halite saturation is only just reached at the highest brine concentrations, but lithium and potassium continue to concentrate demonstrating that these species remain in solution and do not precipitate as solid phase minerals.
Within the nucleus, the mean concentrations are 690 mg/L Li, 5730 mg/L K, and 1050 mg/L B.
Peak values exceed 1000 mg/L Li, 8000 mg/L K and 1200 mg/L B.
Values of this order for Li, K and B are present throughout the salar. The lower tested interval from 54 to 197 m depth tends to have 13 to 36% higher concentrations, with less variation than the upper interval from 0 to 54 m, although the Mg:Li and SO4:Li ratios remain similar for both intervals.
The Salar de Olaroz brine is located in almost the center of glaserite (Na2SO4•3K2SO4) field on the K2 - SO4 - Mg+Li2 Janecke phase diagram. Low ambient temperatures at the Salar will result in the crystallisation of sulphate as glaubersalt (Na2SO4•10H20) in the evaporation ponds, which is stable at low temperatures. The low Mg:Li ratio of the brine allows magnesium removal with slaked lime. The Olaroz brine has high sulphate content (high SO4:Mg ratio), and hence sodium and potassium sulphate salts are likely to crystallise. As the SO4:Mg ratio ratio is >4, there is enough sulphate available in the brine to precipitate the calcium liberated during magnesium removal process.
Published mineral resources (Orocobre website visited June, 2016) were:
Measured resources over an area of 93 km2, to a depth of 54 m, with a mean specific yield of 8.4%.
0.42 km2 of brine @ 632 mg/L Li, 4930 mg/L K, 927 mg/L B, for 0.27 Mt of Li, 2.08 Mt of K and 0.39 Mt of B.
Indicated resources over an area of 93 km2, from a depth of 54 to 297 m, with a mean specific yield of 10.0%.
1.33 km2 of brine @ 708 mg/L Li, 6030 mg/L K, 1100 mg/L B, for 0.94 Mt of Li, 8.02 Mt of K and 1.46 Mt of B.
Measured + indicated resources over an area of 93 km2, from a depth of 0 to 297 m, with a mean specific yield of 9.6%.
1.75 km2 of brine @ 690 mg/L Li, 5730 mg/L K, 1050 mg/L B, for 1.21 Mt of Li, 10.10 Mt of K and 1.85 Mt of B.
This summary is drawn from "Houston, J. and Gunn, M., 2011 - Technical report on the Salar de Olaroz lithium-potash project Jujuy Province, Argentina; prepared for Orocobre Limited, 305p."
The most recent source geological information used to prepare this summary was dated: 2011.
This description is a summary from published sources, the chief of which are listed below.
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Salar de Olaroz
Lopez Steinmetz, R.L., 2017 - Lithium- and boron-bearing brines in the Central Andes: exploring hydrofacies on the eastern Puna plateau between 23° and 23°30′S: in Mineralium Deposita v.52, pp. 35-50.|
Lopez Steinmetz, R.L., Salvi, S., Sarchi, C., Santamans, C. and Lopez Steinmetz, L.C., 2020 - Lithium and Brine Geochemistry in the Salars of the Southern Puna, Andean Plateau of Argentina: in Econ. Geol. v.115, pp. 1079-1096.|
Meixner, A., Sarchi, C., Lucassen, F., Becchio, R., Caffe, P.J., Lindsay, J., Rosner, M. and Kasemann, S.A., 2020 - Lithium concentrations and isotope signatures of Palaeozoic basement rocks and Cenozoic volcanic rocks from the Central Andean arc and back-arc: in Mineralium Deposita v.55, pp. 1070-1084.|
Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.
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