Rio Grande do Sul, Brazil
Cu Ag Au
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The Camaquã sediment hosted copper-silver-gold deposits are located some 230 km to the south west of Porto Alegre, the capital of Rio Grande do Sul in southern Brazil. The mine exploited two separate bodies 600 m apart, the Uruguay and São Luiz deposits (#Location: 30° 54' 30"S, 53° 26' 51"W). Santa Maria, a low grade Pb/Zn deposit within similar hosts is located ~3.5 km to the SW.
The deposits were developed within the late Neoproterozoic to Ordovician Bom Jardim Group within the core of a regional NE-SW trending graben in the Don Feliciano Mobile Belt, Rio Grande do Sul State, southern Brazil. The host Camaquã basin, is generally accepted to have initially been marine, and progressively evolved into a continental setting.
The Bom Jardim Group was deposited at the end of the Dom Feliciano orogeny, part of the Brasiliano Cycle. It is exposed in the Bom Jardim window, the core of a NE (45°) trending domal structure cut by the regional transcurrent NNE (20°) trending Camaquã Fault. The ore is contained within the conglomerate and sandstone facies of host sequence, but not generally in the associated finer rhythmites.
Mineralisation comprises early stage disseminated pyrite within arenites and argillaceous arenites and associated chalcopyrite with minor bornite, generally reaching grades of 0.1 to 0.3% Cu. This is cut by a series of markedly transgressive stockwork zones and by veins up to 50 to 60 cm thick of massive sulphides, hematite-sulphide and quartz-chalcopyrite, which are developed in a zone of fracturing controlled by two oblique intersecting fault systems. The presence of these veins in sections of the mineralised arenites results in grades of 1.3% Cu being achieved, which are mined principally by open cut. Gold is contained within the hematite.
The upper Cu- and Pb-Zn hosting units of the sedimentary sequences of the late Neoproterozoic to Lower Ordovician Camaquã Basin in the Dom Feliciano Belt of southernmost Brazil, were formed during the final amalgamation of the short lived Pannotia supercontinent, and were controlled by large sinistral strike-slip shear zones. Five structural elements have been identified, from the late Neoproterozoic-Lower Cambrian to the Cretaceous, as follows:
• D1 structures, related to a 30° trending, sinistral strike-slip shear zones that controlled the deposition of the mineralised sedimentary Bom Jardim Group and its overlying units, the Santa Barbara/Guaritas Groups, in a transtensional setting. Based on U/Pb in situ methods, the maximum depositional age of the basal section of the Santa Barbara Group is 566±6.9 Ma. The source of detritus within the basin, based on the two main zircon populations, Neoproterozoic and Palaeoproterozoic, is from the eastern and southern parts of the Dom Feliciano Belt, plus reworking of older units of the Camaquã Basin.
• D2 structures are mainly north-south trending shear zones developed during the Cambrian, after deposition of the Guaritas Group.
• D3 and D4 are post-Cambrian, connected to extensional and compressional events related to the breakup of Pannotia and progressive amalgamation of Gondwana and Pangea.
• D5 was related to thermal heating by the Upper Cretaceous continental Paraná flood basalts, heralding the breakup of Pangea/Gondwana, and separation of South America and Africa. Prior to this break-up, the Dom Feliciano Belt abutted, and marked the south-western termination of the NE-SW oriented Damara Belt in Namibia, where it became the Kaoko Belt to the north and Gariep belt to the south, both of which trend NNW-SSE.
The Camaquã copper deposits are hosted by the Late Proterozoic to Lower Palaeozoic Bom Jardim Group within the core of a regional NE-SW trending graben in the Don Feliciano Mobile Belt. The stratigraphic succession is as follows, from the base:
• Crystalline basement - gneiss, migmatite, granulite, amphibolite, granitoid, minor sillimanite gneiss, metabasite and ultramafics.
• Rio Vacacai Sequence - meta-mafics and meta-ultramafics (dunite, peridotite, pyroxenite, gabbro and basalt), minor acid and intermediate meta-volcanics in a lower unit, overlain by pelitic and quartzo-feldspathic schist, with locally developed meta-conglomerate, meta-arkose, conglomeratic phyllite, marble, meta-chert. Intruded by gabbro at 2030 Ma and granitic stocks dated at 1900 Ma.
• Porongos Group - 10 000 m thick - mainly terrigenous detritus represented commonly by schists and pelitic phyllites, quartzite, meta-arkose, metamorphosed marls and marbles. Also present are acid and intermediate volcanics, meta-tuff, meta-chert, graphitic schist, meta-conglomerates, meta-greywacke and lensoid mafics to ultramafics. The Porongos Group is part of a large nappe with tectonic vergence to the west towards the Rio de la Plata Craton.
• Piquiri Gneissic Syenite - dated at 570±37 Ma.
Neoproterozoic to Cambrian
• Bom Jardim or Marica Group - which hosts the Camaquã mineralisation, and comprises conglomerate, sandstone, siltstone, claystone and rhythmite with acid, intermediate and basic volcanics. Deposition has been interpreted as being within a NNE-SSW trending rift under subaerial to shallow water terrigenous to lacustrine conditions. Activation of the faults bounding the reef was accompanied by three phases of basic to acid volcanics intercalated with the coarse terrigenous clastics. Different sources are at variance as to which stratigraphic names and subdivisions apply. Schobbenhaus, et al. (1984) describe the following regional succession:
- Pessegueiro Formation - predominantly arenites and conglomerates with an arkosic matrix, with rounded to subrounded pebbles composed of gneiss, quartzite, quartz, arenite, rhyolite, etc. Intercalated with the arenites are rhythmic alternations of fine siltstones with minor rhyolitic and andesitic tuffs.
- Cerro dos Martins Formation - comprising (after Teixeira and Gonzalez 1988),
+ Arroio dos Nobres Member - predominantly immature conglomerates, arenites and siltstones, which is in turn subdivided into the:
Mangueirao Member, a fine arenites, predominantly greywackes with subordinate arkose, with rhythmic intercalations of siltstone and argillaceous siltstone and minor tuffs. Away from the Camaquã mine area this member may include lower rhyolitic and rhyodacitic extrusives, overlain by conglomerates and sandstones derived from these volcanics; and the
Vargas Member, comprising arenite, mainly fine to medium arkose and conglomerate. This unit hosts the orebodies.
+ Crespos Formation - pink to brown amygdaloidal andesite. Intercalations of this andesite occur in the upper sections of the Vargas Member of the Arroio dos Nobres Formation to the north east.
+ Hilario Member - fissure type explosive pyroclastics and flows of dacitic, andesitic and basaltic composition.
- Acampamento Velho - flows, tuffs and breccias of rhyodacite and rhyolite, acid agglomerates, fine arenites and subordinate siltstones.
• Caçapava Granite, syn and post tectonic granitoids, with different bodies or phases dated at 700 to 610 Ma (syntectonic), 570 to 500 Ma (post tectonic) and 520 to 430 Ma (also post tectonic subvolcanic rocks).
• Camaquã Group - which has horizontal to shallow dip of 5 to 10° and comprises,
- Guaritas (or Santa Barbara) Formation, 2700 m thick - a predominantly red sequence of conglomerate, feldspathic greywacke, sandstone, siltstone and subordinate argillite. Intercalations of andesitic lava have been recorded.
- Coxilha Formation - conglomerates with clasts derived from the Caçapava Granite.
• Extensive sediments of the Paraná Basin.
The Camaquã mines are localised within the Bom Jardim Window which is surrounded by the overlying Ordovician Camaquã Group sediments. The older rocks of the Bom Jardim Group occupy an area of 80 km2 within the Bom Jardim window, which comprises a NE (45°) trending monoclinal structure, which plunges to the north west beneath the Guaritas Formation of the Ordovician Camaquã Group, and is bounded to the south east by a zone of NNE-SSW trending faults, across which is more Camaquã Group sediments. This window occurs within a broader graben/rift which is bounded by a series of faults trending at 20 to 30°. A second set of faults trending at 110 to 130° cuts the graben and are the main loci of mineralisation at Camaquã.
The graben is bounded to the SE by Archaean basement with extensive late Brasiliano (Neoproterozoic to Lower Cambrian) post and syn tectonic granites, while to the NW, it is underlain by both Palaeoproterozoic 'greenstones' of the Rio Vacacai Group and by Archaean crystalline basement cut by the same Brazilian granites. This graben appears to localise the Ordovician Camaquã Group, the Eocambrian Bom Jardim Group, the underlying Neoproterozoic Porongos Group and possibly the Palaeoproterozoic Rio Vacacai Group.
Deposition of the host Bom Jardim Group apparently took place during the Brazilian event, with 650 Ma granitic rocks below and having a similar composition to the Pessegueiro Formation, while sub-alkaline post tectonic granites dated at 510 Ma have contact metamorphosed section of the Bom Jardim Group. Other sub-volcanic rhyolite and microgranites associated with the volcanic rocks at the top of the Bom Jardim Group have been dated at 450 Ma (Teixeira and Gonzalez 1988). More precise SHRIMP U/Pb of zircons from the volcano-plutonic magmatic event of the Bom Jardim Group returned an age of 592±5 Ma (Remus et al., 1999 and sources quoted therein).
The Camaquã orebodies occur as disseminations and veins of Cu sulphides within the conglomerates and arenites of the Vargas Member of the Arroio dos Nobres Formation of the Bom Jardim Group. The Vargas Member, which is believed to represent deltaic sediments, has been subdivided in the mine area, as follows, from the base:
• Lower Sandstone, >400 m thick - fine to medium grained arenites, generally arkosic with intercalations of siltstone and arenaceous conglomerate. Pale grey, grey-green, brown and rose in colour. The principal detrital components are quartz, rock fragments and feldspar. The contacts with the underlying Mangueirao Member and overlying Lower Conglomerate are both gradational.
• Lower Conglomerate, 120 m thick - red, grey green and brown conglomerate with a fine to medium grained sand matrix with intercalations of sandstone.
• Intermediate Sandstone, 20 to 25 m thick - fine to medium grained arenites with local intercalated conglomerates.
• Upper Conglomerate, 200 m thick - crudely sorted conglomerate with clasts, blocks and minor boulders up to 1.5 m in diameter. The clasts are diverse and of similar composition to those found in the other conglomerate units of the Vargas Member, namely granite, quartzite, rhyolite, pyroclastics, schists, quartzo-feldspathic rocks and fragments of various sediments. The matrix is predominantly arenite of arkosic composition.
• Upper Sandstone - the upper most unit of the Vargas Member, with a gradational contact with the underlying Upper Conglomerate. It comprises fine to medium arenites with millimetric intercalations of brown silty argillites, displaying abundant ripple marks and locally mud cracks.
The main sulphide deposits of the Uruguay and São Luiz sectors at Camaquã are located in the upper and lower conglomerates and middle sandstone, while at Santa Maria they are mainly within the sandstones.
In the São Luiz sector the Vargas Member is cut by a steeply dipping dolerite dyke immediately to the SW of the ore zone.
Sulphide mineralisation is present as chalcopyrite, bornite and chalcocite with associated pyrite, occurring in two forms: (i). as disseminations within the host conglomerates and arenites, and (ii). as irregular fault fill massive sulphide veins with a gangue of quartz, hematite and barite.
The various minerals are distributed as follows:
• Chalcopyrite is the most frequent sulphide, occurring either as isolated grains or as intergranular cement in the arenites and conglomerates. It is also present as irregular masses filling fault planes with a gangue of quartz in the São Luiz sector, and hematite in the Uruguay sector.
• Bornite is the second most abundant sulphide and is found principally in the Uruguay sector where it occurs in fault controlled veins with a hematite gangue. It is also present finely disseminated within the sandstones and conglomerates as interstitial cement and is locally the major intergranular cement.
• Chalcocite is the least common Cu sulphide and is principally present as very fine grained intergranular cement. It is seldom seen in the fault controlled veins, although locally in the São Luiz sector it may form significant veins.
• Pyrite occurs mainly as intergranular disseminations within the sandstones and conglomerates, either as individual grains or as irregular masses accompanying other sulphides in veins.
• Other sulphides, such as wittichenite, idaite, molybdenite and carrollite are minor phases.
• Hematite is present as a gangue in fracture fill veins or locally in the gangue of the arenites and conglomerates.
• Gold occurs as inclusions in hematite or chalcopyrite veins.
• Silver is associated with chalcocite and bornite.
• Quartz is the principal gangue in veins of the São Luiz sector, as well as being present as an interstitial cement in the arenites and conglomerates.
• Barite occurs as a gangue within fracture fill veins and locally as nodules accompanying sulphides and hematite.
• Calcite is also present as a widespread cement within the arenites and conglomerates and rarely as veins within faults.
• Chlorite occurs within the matrix of the arenites and conglomerates and as an accessory within the mineralised veins.
• Supergene minerals occur in the weathering zone, including covellite, digenite, antlerite, chrysocolla, brochantite, cuprite, malachite, azurite, tenorite, and native copper. Traces of gold and silver have also been found in the oxidised zone close to surface.
Disseminated mineralisation occurs as follows:
• Chalcopyrite - chalcopyrite, normally accompanied by pyrite, occurs as isolated grains within green, grey or pink conglomerate. Normally these dissemination are of a low tenor (0.1 to 0.3% Cu), although locally they may occur as important concentrations of intergranular cement.
• Bornite - fine spots of bornite (with or without chalcocite and chalcopyrite) are found in green coloured conglomerate or as a crude cement between the clasts of green to brown conglomerate. Locally bornite may constitute the principal cement occupying the total intergranular space.
• Chalcocite - fine spots of chalcocite occur irregularly dispersed through, or finely dispersed along the stratification of fine conglomerates and arenites which are flesh to pale grey to rose tinged green in colour. Locally bornite and chalcopyrite are associated.
Teixeira and Gonzalez 1988 argued there was evidence of a diagenetic origin of the disseminated sulphides, as follows:
• The presence of sulphides among and surrounding detrital quartz grains and as their authigenic cement.
• The widespread presence of finely disseminated sulphides unrelated to faulting.
• The presence of sulphides in the clasts of an intraformational conglomerate with a barren matrix.
• The local concentration of sulphides in diagenetic structures.
• The zonation of minerals relative to sedimentary facies, with the Camaquã Cu being within coarse conglomerates and arenites and Santa Maria Pb/Zn mineralisation hosted by fine arenites, within the same deltaic fan.
The disseminated Cu sulphides are generally of a low tenor and only locally attain significant grades, with zones containing veins having enriched Cu levels compared to intersections with only disseminations.
The disseminated mineralising sequence at Camaquã has been interpreted to comprise, (modified after Gomes, pers. comm., May 1992):
• Initial introduction of diagenetic intergranular pyrite, and intergranular and grain coating calcite,
• Albitisation of K feldspar,
• Introduction of Cu and the production of ankerite (presumably from the combination of Fe, Mg and/or Mn accompanying the Cu), resulting in interstitial Cu sulphides and ankerite accumulations. Fe oxides would be formed by the progressive replacement of pyrite by chalcopyrite, chalcopyrite by bornite and bornite by chalcocite, giving the rocks a red tinge.
From the information perused, it is unclear whether the disseminated mineralisation precedes the veining or is due to fluids percolating outwards from the vein stage.
Mineralised veins within the zone of disseminated sulphides, apparently fall into the following groups:
• Massive sulphide veins - generally bornite and chalcopyrite, in which the sulphide fills most of the fracture, with little accompanying gangue, commonly being as thick as 50 to 60 cm. Chalcocite may locally accompany bornite in veins of up to 1 to 5 cm.
• Hematite-sulphide veins - chalcopyrite and bornite with variable amounts of accompanying hematite.
• Quartz and chalcopyrite veins - chalcopyrite is usually the dominant sulphide, with chalcocite at times and rarely bornite. The only gangue is quartz, whilst the rocks enclosing the veins are invariably silicified for 50 cm on either side of the vein.
In the veining, primary ore formation appears to be the result of multiple mineralising events (Laux et al., 2005). In each discrete mineralising event, quartz was the first mineral to form, followed by pyrite, chalcopyrite and bornite. Carbonate and barite were precipitated by the end of the event. Sulphur isotope analyses of pyrite, chalcopyrite and bornite show little variation, with δ34S CDT clustering around 0‰ (-1.8 to +0.6‰), indicating a magmatic origin for the sulphur. However, δ34S values of +10.30 to +14.24‰ for sulphur in barite indicate probable oxidation due to the mixing of magmatic and meteoric SO42- rich fluids. Analyses of Pb isotopes in chalcopyrite, pyrite and bornite from the Camaquã deposit plot conformably with the reference isochron of 592 Ma calculated for regional igneous rocks (SHRIMP U/Pb zircon analyses) specifically the Lavras-Caçapava granite (Laux et al., 2005).
Microthermometric measurements in fluid inclusions of quartz veins indicated temperatures varying from 236 to 60°C. Fluid inclusion in carbonate displayed trapping temperatures between 150 and 50°C, whereas the trapping temperatures in barite are below 80°C during the final stages of fracturing when circulating fluids mixed with meteoric waters. The fluid salinity has a large variation from one mineral to another: 2.7 wt.% NaCl equiv. to near pure water in quartz; 14 wt.% NaCl equiv. in carbonate; 8 to 10 wt.% NaCl equiv. in barite. The structural control of mineralisation, the occurrence of superimposed mineralising events, the temperature of deposition of the early-formed ore minerals (190 to 330°C), and the sulphur isotope ratios, indicate that the vein mineralisation of the Camaquã Mine may be considered to be of hydrothermal origin, the result of distal magmatic fluids focused into a relatively oxidised clastic succession (Laux et al., 2005).
Pb isotope data from sulphides at Camaquã and Santa Maria suggest metals were largely derived from a crustal source with very primitive Pb at the end of the Brasiliano cycle and Remus et al. (1999) suggest mineralisation is related to late to post-orogenic Brasiliano magmatic event, possibly the Lavras or Caçapava granite plutonism. However, the metal was largely derived from old basement and sedimentary rocks of the Bom Jardim Group by circulating magmatic fluids.
• Sulphide bearing veins were emplaced in structural open spaces produced by the NW-SE to WNW-ESE faulting. If this was merely remobilisation and upgrading of earlier disseminated sulphide (by a bulk factor of at least twice), depletion of the disseminated zone should be apparent. The veins appear to represent a second pulse of Cu mineralisation after compaction (the first phase may be prior to lithification), with deposition in brittle fracture openings.
The limited literature available does not mention the presence or absence of any redox front or the lateral and vertical persistence of pyrite and Cu sulphides.
The Uruguay sector orebody occupies a volume of approximately 900 x 600 m by 700 m in depth. Lodes occur in sets with individual strike lengths of up to 600 m and thicknesses of up to 2 m. The principal characteristic of this zone is the intense fracturing by a NW-SE to WNW-ESE trending fault set. The principal fault orientations are 280 to 300°strike, dipping at 70 to 80°NE (associated with breccia and cataclastic rocks) and 290 to 310°strike, dipping at 50 to 70°SW (associated with brecciation). These two fault directions formed a zone of stockwork fracturing and brecciation which cuts the main sediment hosted mineralisation within the conglomerates and arenites. Mineralisation in these veins extends from near the base of the Lower Sandstone, to the surface in the Upper Conglomerate.
In the Uruguay sector, the NW quadrant is the most economically important. On the eastern margin local extensions of disseminated chalcocite and bornite with or without thick veins of bornite are characteristic of the ore, while the SE portion is represented by low tenor disseminations of chalcopyrite and pyrite with veins of chalcopyrite in a gangue of hematite and less frequently quartz. To the SW, disseminated mineralisation extends to the Cemiterio Fault.
Mineralisation in the São Luiz sector is present over an area of 700 m length in the NW-SE direction, with a width of 20 to 110 m, with the more important vein mineralisation being confined to the vertical interval where the fault system cuts the Upper Conglomerate and the Intermediate Sandstone. Quartz veins with chalcopyrite predominate, although chalcocite is found in the NW of the sector. Veining is controlled by the conjunction of three directions of faulting, namely, at 335 to 350°strike, dipping 70 to 80°NE; at 300 to 310°strike, dipping 70 to 80°NE; and 270 to 290°strike, dipping 70 to 80°SW. The economic mineralisation only extends for a short distance into the Lower Conglomerate. The principal fractures carry very rich vein ore over widths generally of 10 to 15 m. The disseminated mineralisation with economic grade generally comprises chalcocite and occurs on the south west of the zone of veining, principally in the top of the Lower Conglomerate over a thickness which is very variable, but generally within the range of 1 to 15 m.
At both the Uruguay and São Luiz sectors, the orebodies have a conical form, and a lateral and roughly horizontal zonation of sulphides along NW trending fractures hosted lodes. Pyrite, chalcopyrite and hematite (with gold) occur in the SE, and chalcocite and bornite to the NW. At Uruguay, chalcopyrite and pyrite dominate at depth.
Alteration is manifested as a change in colour of the arenites and conglomerates, from their original brown to a pink and then greenish colour, reflecting a progressive increase in chlorite, silica, albite, carbonate and sericite. At Uruguay, chlorite and sericite dominate, while at São Luiz alteration is predominantly silica and sericite.
Age dating of eleven samples of clays (illite) from both the São Luiz and Uruguay sectors ore veins in faults yielded ages of 457 and 474±11 Ma and 350±8 Ma (Bonhome and Ribeiro, 1983). This is younger than the interpreted Eocambrian age of the host sediments. Earlier K/Ar determinations on diagenetic clay minerals in the host Arroio dos Nobres Member yield ages between 535±16 and 527±17 Ma (Bonhome and Ribeiro, 1983).
At Santa Maria, ore occurs in three zones. The third zone contains 56% of the ore, which is a polymetallic Pb-Zn-Cu with by-product Ag and Cd, with Cu and Ag enriched intervals at the base of the conglomerate unit, while Pb is concentrated near the conglomerate-sandstone contact and Zn in the sandstone. The principal ore minerals are galena and sphalerite, occurring as dissemination in arenites and conglomerates, or as massive lodes, cutting the stratigraphy in 330 to 350° trending fractures. Sphalerite and galena intergrowths are common. In places galena is surrounded by sphalerite, which is in turn wrapped in galena. Chalcopyrite occurs as intergrowths with sphalerite, and is surrounded by bornite and chalcocite. Pyrite is most abundant outside of the mineralised zone, commonly being replaced by sphalerite and galena (Remus et al., 1999 and sources quoted therein). Homogenisation temperatures in primary inclusions in sphalerite and carbonates fall between 289 and 117°C (mean 210°C), while secondary fluid inclusions in quartz have temperatures of 160 to 90°C (mean 137°C). Geothermal calculations based on S-isotopic fractionation between galena-sphalerite pairs yield a temperature of 280 to 301±20°C, whilst microprobe data for ore related chlorite in matrix arenites give temperature estimates of 315 to 268°C (Remus et al., 1999 and sources quoted therein). δ34S CDT values from Santa Maria range from -2.6 to +1.1‰, indicating a magmatic origin for the sulphur (Remus et al., 1999 and sources quoted therein).
The published reserves/resources + production at Camaquã in 1988 were (Teixeira and Gonzalez, 1988):
30 Mt @ 1.1% Cu, 0.4 g/t Au, plus past production of 8.3 Mt.
The annual production in 1990 was around 1.75 Mt per year taken from two separate bodies, the larger Uruguay and smaller São Luiz sectors. The Uruguay sector body was initially mined by an open pit some 900 x 400 m in area by 250 m deep, but subsequently by underground methods, connected to the São Luiz underground operation. In 1985 open pit production was 1.12 Mt @ 0.49% Cu, with 3.7 Mt of waste, with a further 0.63 Mt from underground. The planned overall mining grades are 0.76% Cu (to a 0.3% Cu cut-off) in open cut and 1.11% Cu (to a cutoff of 0.6% Cu) underground. The mine was closed in 1996.
The low grade Pb/Zn deposit, Santa Maria, ~3.5 km to the SW within similar hosts, had resources of the order of 30 Mt @ 2 to 3% Pb+Zn.
Most of this summary, unless indicated otherwise, is derived from Teixeira and Gonzalez 1988 which is in Portuguese.
The most recent source geological information used to prepare this summary was dated: 2005.
Record last updated: 17/4/2015
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
References to this deposit in the PGC Literature Collection:
Laux J H, Lindenmayer Z G, Teixeira J B G and Neto A B 2005 - Ore genesis at the Camaqua copper mine, a neoproterozoic sediment-hosted deposit in Southern Brazil : in Ore Geology Reviews v26 pp 71-89|
Remus M V D, Hartmann L A, McNaughton N J, Groves D I, Reischl J L, Dorneles N T 1999 - The Camaqua Cu(Au, Ag) and Santa Maria Pb-Zn (Cu,Ag) mines of Rio Grande do Sul, Southern Brazil - is their mineralization syngenetic, diagenetic of magmatic hydrothermal: in Silva M G, Misi A (Ed.), 1999 Base Metal Deposits of Brazil CPRM, Brazil pp 54-63|
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