Mina de Cobre Panama - Petaquilla, Botija, Colina, Valle Grande, Brazo, Molejon
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The Mina de Cobre Panamá cluster of copper-molybdenum-gold deposits, including, Colina/Petaquilla, Botija, Valle Grande, Brazo and Botija Abajo, and the related Molejón epithermal gold deposits, are distruibuted over a NW-SE elongated area of ~10 x 5 km, located in the Donoso District of Colón province, Republic of Panamá, ~120 km west of Panamá City and 20 km south of the Caribbean Sea coast (#Location: 8° 49' 32"N, 80° 39' 28"W).
Tectonic and Regional Setting
See the Cerro Colorado (Panama) record for the tectonic and geological setting of eastern central America.
The oldest rocks in the Cobre Panamá deposits area are submarine andesitic and basaltic flows and tuffs, with intercalated clastic sedimentary rocks and reef limestones, of probable Eocene to early Oligocene age. The arc became emergent during the mid-Oligocene, when terrestrial flows and volcaniclastic rocks with lesser intercalated submarine tuffs ppear within the sequence. Subsequent Miocene and younger rocks make up the bulk of volcanic rocks in western Panama, comprising both terrestrial and marine volcanic and volcaniclastic rocks with progressively increasing felsic composition (Rose et al., 2010).
These mid-Tertiary rocks are intruded by the 36.4±2 Ma mid-Oligocene (hornblende K-Ar; Kesler, 1977) predominantly granodioritic Petaquilla batholith that hosts most of the copper mineralisation of the district. Numerous satellite apophyses, stocks, plutons and dykes of equigranular to porphyritic granodiorite, tonalite, quartz diorite and diorite occur around the margin of the batholith, mostly along its southern boundary. A feldspar-quartz-hornblende porphyry is the most extensive of these porphyry lithologies, containing slightly higher grade copper mineralisation than the granodiorite. There are few cross-cutting contacts between the feldspar-quartz-hornblende porphyry and the granodiorite, which are locally difficult to texturally distinguish, suggesting they were intruded over a short period, most likely as a continuum of differentiation products of the regional scale batholith. A volumetrically minor set of feldspar quartz porphyry dykes were subsequently emplaced, only recognised at the Botija and Brazo deposits. A set of volumetrically very minor mafic dykes cuts the all of these lithologies, and may be a final differentiation phase of the batholith. A set of late andesite dykes with well-developed chill margins cross-cuts all other lithologies. Since exhumation of the porphyry system, a tropical saprolite profile has developed (Rose et al., 2010).
The feldspar-quartz-hornblende porphyry bodies at Botija, Colina and Valle Grande have lopolith morphologies, indicated by the abundance of roof pendants, the often flat-lying geometry of the lower porphyry contact, the proximity of a large batholith and likely underlying magma chamber, the deflation of which would be capable of allowing subsidence of the lower contact, and the presence of fracturing at the lower porphyry contact without significant displacement. At Botija and Colina the feldspar-quartz-hornblende porphyry is interpreted to have flowed laterally into a sill-like lopolith fed from a high-angle feeder dyke in the north of the deposit. At Valle Grande emplacement was likely fed from a high-angle feeder dyke to the northwest (Zák et al., 2006), consistent with the interpretation that the feldspar quartz hornblende porphyry in the three deposits formed as a differentiation product of the larger granodiorite batholith (Rose et al., 2010).
The dominant structural trends are northeast and northwest, with the latter being parallel and possibly related to the Canal shear zone and other major sinistral shear zones in the region.
The principal lithologies, as described by Rose et al. (2010) are:
Andesite, a light green, chlorite-altered, fine-grained andesite that is weakly magnetic and comprises mostly massive flow units that are bounded by fragmental flows, with lesser lapilli tuffs and volcanoclastic interbeds.
Granodiorite, which is a mottled white-grey, medium-grained equigranular rock with interlocking crystals of white feldspar hornblende and quartz, containing subrounded to subangular, centimetric-scale fine-grained mafic xenoliths and occasional aplite dykes. Local white clay alteration produces a pseudo-porphyritic texture by altering the minerals surrounding feldspar crystals.
Feldspar Quartz Hornblende Porphyry, a light grey porphyritic lithology with a crowded porphyry texture, which does not always have a significant difference in grain size between the groundmass and phenocrysts. The groundmass is light grey, fine-grained, and contains feldspar with subordinate mafics and quartz. Phenocrysts comprise crowded white subhedral to euhedral feldspar (often plagioclase) phenocrysts, lesser clear glassy anhedral quartz "eyes" and minor hornblende.
Feldspar Quartz Porphyry, a light grey porphyritic rock with a light grey, aphanitic and siliceous groundmass containing crowded white subhedral to anhedral feldspar phenocrysts and clear, glassy anhedral quartz "eyes" and very rare bi-pyramidal quartz phenocrysts.
Feldspar Hornblende Porphyry, a light green-grey porphyritic rock of andesitic composition, with a light grey, fine-grained groundmass containing dominant white subhedral to euhedral feldspar (mostly plagioclase) and subordinate dark green hornblende and lesser quartz. It also contains sparse, centimetric, irregularly shaped, medium-grained mafic xenoliths.
Mafic dykes, a dark green, pervasively chlorite altered, fine-grained mafic pyroxene porphyry with local chilled margins.
A Saprolitic profile covers much of the area below a thin (1 cm to 10 m) layer of black organic material and generally <1 m of residual soil, which in turn overlies the 1 to 20 m thick layer of orange to white (oxidised) or green (reduced) saprolite. The saprolite layer is generally deeper over andesite relative to intrusive rocks. The saprock transition from saprolite to relatively fresh andesite typically occurs over an interval of less than a few metres, while the transition zone to relatively fresh granodiorite may occupy several tens of metres.
Five types of alteration are associated with mineralisation at Botija, Colina, and Valle Grande, described below (after Rose et al., 2010) in the order of development in the hydrothermal system:
Propylitic alteration, type A, which is chlorite dominated, accompanied by accessory epidote, pyrite, and calcite, and is best developed within the andesite volcanic wall rocks.
Propylitic alteration, type B, characterised by chlorite and silica which occur in approximately equal intensity, producing much harder rocks that other alteration types. In the porphyritic lithologies, chlorite generally affects ferro-magnesium phenocrysts while silicification appears to primarily affect the groundmass. Pyrite and sericite (often green-coloured) may also be present. This style of silica-chlorite alteration appears to occur at depth within the deposits but is also found at shallow levels in the peripheral zones.
Potassic alteration, mainly in the form of K feldspar selvedges to quartz±sulphide veinlets and as irregular patches, although K feldspar flooding is rare. In addition, fine-grained secondary biotite alters ferro-magnesium minerals such as hornblende and magmatic biotite, and occurs in discontinuous veinlets that commonly contain magnetite, chalcopyrite and rare bornite. Millimetric magnetite-only veinlets are uncommon, but are known within the potassic alteration zone. The degree of potassic alteration is largely determined by the feldspar or biotite abundance of the protolith. Anhydrite veinlets that are generally of millimetric thickness, commonly accompany potassic alteration, particualrly in the deeper parts of the deposit, although at depths of less than ~200 m below the surface, have hydrated to gypsum.
Phyllic alteration, occurs as sericite alteration of all rock-forming silicate minerals, with associated silicification and pyrite. This style of alteration occurs irregularly in the upper 150 to 200 m of all of the deposits but is often difficult to recognise through different protoliths and earlier alteration facies. Where the fluids responsible have been drawn down into permeable structural zones, it may persist to much deeper levels. Phyllic alteration occasionally includes chlorite, with both green and white sericite occurring within this zone, apparently related to distinct alteration events. Sericite is a collective term for white phyllosilicate, with a wide range of grain size from very coarse, granular, millimetric muscovite, to very fine grained "silky" textured. Phyllic alteration is ubiquitous, occurring as white sericite-altered selvedges to quartz-pyrite veinlets that frequently contain minor chalcopyrite.
Argillic alteration, which is frequently found in the upper parts of the deposits where it is largely coincident with phyllic alteration, making visual differentiation of clay or sericite dominant alteration difficult. The clay minerals range from white to buff or light brown, and include kaolinite, smectite and illite.
Paragenetic, cross-cutting and textural relationships suggest the two propylitic and the potassic mineral assemblages formed early, and that both frequently accompany chalcopyrite, minor bornite and minor pyrite mineralization. These early phases are overprinted by phyllic alteration that includes white and green sericite and ubiquitous pyrite with variable silicification or quartz veining. Phyllic alteration is frequently accompanied by chalcopyrite, in addition to pyrite, but very rarely by bornite. The argillic assemblage, which generally occurs within 300 m from surface, overprints propylitic, potassic and phyllic alteration, and is most common near surface. White clay found within a few tens of metres of oxidised sulphides is most likely supergene in origin, possibly overprinting an earlier alteration phase (Rose et al., 2010).
Additional to these five dominant alteration styles, metasomatism can produce a biotite hornfels within the andesite volcanic package, with significant disseminated sulphide mineralisation that may be broadly coeval with the propylitic and potassic stages. Post-mineral zeolite alteration of the intrusions and andesite is widespread and occurs as pink zeolite veinlets and fracture fillings with vein-hosted calcite and rare barite, locally comprising as much as 10% of the mass. This likely occurred late in the development of the phyllic alteration, before hypogene clay alteration ended. Chloritisation of mafic minerals may also accompany this late-stage mineral assemblage (Rose et al., 2010).
The characteristics of the individual deposits may be summarised as follows:
The Botija deposit covers a WNW-ESE aligned 2 x 1 km area where the granodiorite batholith and the feldspar-quartz-hornblende porphyry host two irregular, keel-shaped andesite roof pendants, each ~500 m in diameter and separated by approximately 300 m of intrusive. These pendants are supported, but not cross-cut, by the intrusions, suggesting the latter was emplaced relatively passively by magmatic stoping, rather than as a stock that cross-cuts pre-existing lithologies. The roof pendant in the central part of the deposit extends to a depth of 200 m, while the other, which forms an embayment into the eastern margin of the batholith, situated at the eastern side of the deposit, persists to a depth of at least 300 m. A smaller north-south oriented ~250 m x 100 m andesite roof pendant on the northern margin of the deposit, extends to a depth of ~150 m. The feldspar-quartz-hornblende porphyry has been intruded as one to four dykes, each ranging in thickness from 20 to 200 m, that coalesce to form a single body between 100 and 600 m thick, extending to a depth of approximately 450 m. Overall, near the surface, this feldspar-quartz-hornblende porphyry forms an irregular set of dykes to stocks over an area of ~1500 x 700 m.
In a general sense, mineralisation is spatially associated with this intrusive porphyry phase. The morphology of the feldspar-quartz-hornblende porphyry suggests it was intruded from the north as a series of generally 70°N dipping dykes that coalesced and fed the central apophysis. There is very little hydrothermal or magmatic brecciation.
Potassic alteration is widespread in the centre of the deposit, with a loose spatial association between higher copper grades and porphyry intrusion, often following the northerly dip of these features. Propylitic alteration is irregular and is not dominant, generally occurring sporadically at depth and in the periphery of the deposit, where it specifically overprints andesite. Phyllic alteration is irregular, mainly occurring near surface in the central part of the deposit, but also at depth. Argillic alteration is also irregular, and is mostly within 250 m of the surface.
Faulting only displaces the lithologies by a few tens of metres, and mineralisation and alteration are not significantly displaced. Zones of increased fracturing were noted on the southern margin of the deposit, following the Botija River Fault Zone (Speidel and Faure, 1996), although no evidence of displacement is observed. Faulting and fracturing trends at 70 to 90 and 300 to 330° and mostly dip to the north, commonly containing pyrite and sometimes chalcopyrite, frequently with chloritic and sericitic feldspar-quartz porphyry dykes in the western part of the deposit area (Escalante, 2009). Another centimetric, 160 to 180°, 20 to 60°E dipping fault set may control the distribution of chloritic, sericitic, and clay-altered feldspar-quartz porphyry dykes and local quartz veining in the northern and southern parts of the deposit (Escalante, 2009). One of these faults may also mark the southern contact of the eastern andesite roof pendant (Escalante, 2009). Many of the minor faults and fractures may have resulted from dilation, particularly in the subsiding floor of the lopolithic feldspar-quartz-hornblende porphyry.
A quartz vein stockwork of A- and B veinlets occurs within the central feldspar-quartz-hornblende porphyry dyke complex, particularly in its contact zones, and appears to form the locus of higher-grade copper and molybdenum mineralisation. This stockwork hosts most of chalcopyrite and bornite mineralisation, with the B-veinlets containing the bulk of the molybdenite. In the SE and northern parts of the deposit, narrow zones of epidote and chlorite skarn up to a few tens of metres across occur at the andesite contact accompanied by specularite, chalcopyrite, pyrite and often calcite, quartz, bornite and magnetite veinlets, blebs, and disseminations. Secondary chalcocite and covellite have been observed near the upper contact of the sulphide zone.
Colina (previously Petaquilla)
The ~2.5 x 1 km Colina deposit, which is ~3 km west of Botija, is focused on an east-west to WNW-ESE aligned, lopolithic feldspar-quartz-hornblende porphyry sill and dyke complex with comparable dimensions. An irregular, L-shaped andesite roof pendant is located in the southern part of the deposit, the long axis of which is orientated ESE. At the surface, the long and short axes of the pendant are 100 to 200 m and 400 to 500 m wide respectively. The majority of the feldspar-quartz-hornblende porphyry comprises 50 to 200 m thick sills that dip shallowly to the north, often interconnected by dykes, which coalesce in the centre of the deposit. The basal margins of the feldspar-quartz-hornblende porphyry sills are often gradational with the underlying granodiorite, accompanied by increased fracturing, frequently with minor mafic dykes, and commonly a rapid decline in copper grade. Towards the northern margin of the intrusive complex, the granodiorite and andesite host rocks are intermixed, and the nature of the contact and morphology of the granodiorite are complex.
There is very little potassic alteration at Colina compared to Botija, but where present, occurs as weak potassium feldspar with patchy biotite alteration of mafic minerals. Propylitic alteration generally affects the andesite in the periphery of the deposit, while in the central part the andesite is frequently altered to a silica-chlorite assemblage. Weak phyllic alteration is common, but is patchy and discontinuous, and in general is not associated with the higher-grade part of the deposit, although it is generally found to mantle the elongate core zone of higher-grade copper mineralisation. Anhydrite and its (supergene) alteration product, gypsum, are also not as common as they are at Botija. Magnetite is more common at Colina than Botija in the western and northern parts of the deposit, and an area of quartz-magnetite veining follows one of the thicker sills. Argillic alteration forms as an often-continuous zone from surface to depths ranging from 20 to 80 m. It is most likely of supergene origin. Late, mostly fracture-filling zeolite and calcite alteration is widespread. No significant faults have been mapped at Colina.
Higher copper grades appear to generally be loosely spatially associated with feldspar-quartz-hornblende porphyry, particularly where dykes and sills coalesce into larger masses, and around the upper contacts of the sills. The deposit consists of several thin, stacked sheets of high-grade mineralisation (spatially coinciding with the sills), separated by areas of low-grade. Pyrite and chalcopyrite, with lesser bornite, mainly occur in quartz veinlets, frequently with molybdenite. Contact metamorphism forms strongly silicified or biotite-altered zones where andesite is in contact with feldspar-quartz-hornblende porphyry. Pyrite and chalcopyrite are generally found in veinlets with lesser blebs and disseminations. Magnetite and molybdenite have also been noted in the same zones, the latter occurring in quartz B-type veinlets. Secondary chalcocite and covellite occur as sooty coatings, primarily on chalcopyrite at the base of the saprolite zone, or within partially oxidised structures that penetrate more deeply into the underlying sulphide domain, following permeable structures. Occasionally chalcocite has completely replaced the pre-existing sulphide to form veins and disseminations. Native copper rarely occurs in fractures. Locally, within the saprolite or secondary copper zones, malachite is observed where a copper sulphide mineral has been oxidized. Secondary chalcocite and covellite have been observed near the upper contact of the sulphide zone.
The WNW-ESE oriented, 2 x 1 km Valle Grande deposit, which is <1 km SSE of Colina, is focused on a 2000 x 500 m wide, irregular feldspar-quartz-hornblende porphyry lopolith that trends to the southeast. An irregular, ~300 m diameter andesite roof pendant is located at the southeastern end of this body. The northeastern contact of the lopolith is interpreted to be irregular but is generally vertical, while the southwestern contact dips to the NE, resulting in the body widening towards the surface. Along its southwestern contact, the lopolith branches into various 10 to 200 m wide discontinuous sills that intrude the andesite and lesser granodiorite) host rock at low angles locally approaching horizontal, possibly representing the feeder dyke tothe lopolith.
Potassic alteration is generally erratically distributed and often occurs at depths of at least 200 m, with the thickest, most coherent development in the central part of the principal dyke. The main alteration type is propylitic, most likely reflecting the dominance of andesitic hosts, and the assimilation of these rocks into the feldspar-quartz-hornblende porphyry. Silica-chlorite alteration is irregular, often occurring deep within the feldspar-quartz-hornblende porphyry dykes. Phyllic alteration is irregular and occurs generally on the contacts of the feldspar-quartz-hornblende dyke, mantling it in some drill sections. Argillic alteration occurs from surface to depths of 100 to 150 m, often as a continuous zone. Sporadic areas of patchy, deep (200 to 300 m) argillic alteration are intersected in drilling. Clay that begins at surface is likely to be at least partly supergene, and the isolated, deep patches of clay alteration may be hypogene in origin. No specific structural features have been delineated.
Higher-grade copper mineralisation occurs along the flanks of the lopolith, following the feldspar-quartz-hornblende porphyry contacts, where quartz-sulphide veinlet densities are high. Conversely, copper grades and quartz-sulphide veinlet densities are lower within the central axis of the dyke. This area corresponds to an elongate, low-grade core of the copper porphyry system.
The Brazo zone is 3 km SSE of the Botija deposit, 4 km ESE of Valle Grande, and is outlined by a well-defined Mo geochemical soil anomaly. Porphyry-style Cu-Au mineralisation, occurs within a feldspar-quartz porphyry, accompanied by pervasive sericite and/or clay alteration with pyrite and quartz and Well-developed quartz stockwork veining. Supergene mineralisation comprises chalcocite and rare native copper, extending locally to a depth of 150 m. Hypogene mineralisation is chalcopyrite, pyrite and rare bornite. The mineralised zone has a southeastern trend with dimensions of at least 300 x 200 m, and extends to a depth of 350 m.
This zone is 2 to 3 km southeast and along strike from the Botija deposit and 1 to 2 km northeast of the Brazo zone. Gold-enriched porphyry copper mineralisation is hosted in feldspar-quartz-hornblende porphyry and andesite tuffs and flows. Alteration is dominated by an argillic assemblage of kaolinite, quartz and pyrite, which is cross-cut by stockworks of quartz and chalcedony. Supergene mineralisation occurs to depths ranging between 10 and 80 m and consists of fracture-controlled and disseminated chalcocite. Rare native copper has also been encountered. Hypogene mineralisation consists of chalcopyrite, pyrite and rare bornite and covellite. Two zones of mineralisation are recognised, "Botija Abajo West" and "Botija Abajo East". Mineralisation at Botija Abajo West covers an area of ~500 x 350 m, extending to at least 140 m depth, and is dominantly copper rich with local Au-enriched zones. Botija Abajo East is a southeast-trending 650 x 150 m zone that extends to a depth of ~50 m.
Molejón Gold Deposit
The Molejón gold deposit is hosted within the Miocene Cañazas Group, a thick undifferentiated sequence of andesites, andesitic basalts and tuffs, which in the deposit area include massive andesite flows, feldspar porphyritic andesites, andesitic tuffs and agglomerates. The deposit is located near the southern margin of the major, NW-SE elongated 20 x 10 km, Late Tertiary granodiorite-quartz monzonite Petaquilla batholith, outcropping to the northwest of the mine area. The host sequence has been intruded by quartz-feldspar and feldspar porphyries.
The main lithologies from the immediate deposit area have been described as follows (Lufkin, in: Muller, 2007):
Andesitic Rocks - greenish andesitic porphyry with micro-phenocrysts altered to sericite, chlorite and opaque minerals. The rock is locally veined and brecciated with quartz. Quartz veins may contain abundant, disseminated sericite and be cut by carbonate. Magnetite and hematite are the dominant opaques followed by pyrite and traces of chalcopyrite and bornite. Alteration may be strong, with a very fine quartz-chlorite-clay matrix with argillized feldspars and mafic minerals converted to chlorite with associated magnetite and pyrite.
Quartz Feldspar Porphyry - altered quartz feldspar porphyry rock with sericitised feldspars and opaques minerals as veinlets of pyrite, chalcopyrite, disseminated iron oxides, mostly goethite and traces of sphalerite.
Altered Rock - strongly silicified rock with veinlets and pods containing quartz carbonate and sericite. Opaque minerals, ~1 to 2% include pyrite, chalcopyrite, pyrrhotite, galena and sphalerite, as well as traces of tetrahedrite, gold and iron oxides in the form of limonite/goethite and hematite.
On a district-wide scale, two major structures are evident, i). a NE-SW fracture trend that seems to control the main Molejón quartz breccia, and connects Molejón with the Botija Abajo and Brazo zones, and ii). a NNW-SSE structural feature that passes through both the Valle Grande and Molejón deposits.
The strong weathering has formed a thick cover of saprolite, with outcrops of unoxidised rock very rare, largely restricted to creek beds and the Molejón open pit. The saprolite is overlain by a shallow organic soil, and varies depending on the original rock, but typically outcrops as a light brown to yellowish argillised quartz breccias, to reddish where pyrite or other iron rich minerals were present and to light green-brownish where andesite was the original rock. It is basically composed of soft clays, a mixture of quartz, kaolinite, illite and sericite, with abundant quartz relics in the mineralised structure. The transition zone from saprolite to fresh rock is soft and may show the texture and color of the underlying rock. The saprolite layer varies from zero to a few metres in topographic lows and up to 20 m in some of the upper pit benches. It is shallow over andesitic bedrock and particularly deep in fault zones.
Gold and silver mineralisation at Molejón is associated with generally shallow-dipping silicified tabular zones along the NE-SW (Main) and NNW-SSE (NW) structural zones, represented by a relatively high-level hydrothermal system of epithermal veins and breccia zones with quartz and quartz-calcite filling generally enclosed in andesite, andesite porphyry and quartz-feldspar porphyry.
The Main Zone is a NW dipping tabular structure with a strike length of ~1100 m near surface, and a down-dip length of 450 m, dipping at 30°, apparently becoming sub-horizontal at an elevation of 50 m below sea level. The width of the main structure can be as much as 75 m near surface, but tends to diminish at depth. The Northwestern Zone of the deposit is characterised by a tabular structure similar to the Main Zone but with a tendency to be sub-horizontal to the southeast, to eventually coalesce with the Main Zone.
The breccia zones, which are commonly parallel to volcanic bedding, may also have associated stockwork and thicker quartz veins, as well as associated silicification and brecciation in adjacent volcanic units. Mineralisation is also closely related to several large, NE-trending quartz-feldspar porphyry dykes. A major NE-trending fault system, which extends from Botija Abajo through Molejón, is the main structural control for the quartz solution fill of the breccia hosting the majority of the hypogene gold mineralisation, although not all silicified and/or brecciated rock is well-mineralised. The best gold grades are associated with three structurally controlled zones of quartz-carbonate breccia and adjacent altered zones within the associated quartz-feldspar porphyry dykes, which are similar in nature to late syn-mineral dykes intruding the Colina/Petaquilla west zone and Valle Grande. Very little sulphide is associated with this deposit (S. Muller, 2007). Unlike the porphyry mineralisation of the district, very little copper is recorded at Molejón.
Quartz fill is commonly milky white to greyish in colour, with banded texture. The nature, textures and cross cutting nature of the different types of quartz present suggest that mineralisation occurred in multiple stages.
Weathering and intense oxidation has played an important role in the near-surface distribution of gold mineralisation. Kaolinite is particularly rich in the saprolite on top of the Main Zone structure, while the rest is high in iron oxides as hematite and magnetite. Other oxide minerals that can be observed at surface are goethite and pyrolusite. It is apparent that quartz breccias are commonly vuggy and limonitic, and tend to be preferential host rocks for the gold. This more siliceous rock tends to form small hills and ridges due to its resistance to erosion in a high rainfall environment. The country rock adjacent to the low-angle faults also tends to be locally silicified and also is relatively resistant (AAT, 2007). Gold mineralisation has also been reported in the clayey section of saprolitic soils, although this has been irregular, and economic metallurgical recovery is uncertain.
Fee gold crystals and electrum occur as minute inclusions in crystals of chalcopyrite and isolated in calcite and quartz veins, which are present along with minor amounts of pyrite, chalcopyrite, pyrrhotite, galena, sphalerite, traces of tetrahedrite and gold below the zone of oxidation, while in the oxide zone, the gold and silver is associated with iron oxides in the form of limonite/goethite and hematite. Much of the known mineralisation, including that with the highest values, occurs in near-surface, oxidised quartz breccias.
Published NI 43-101 compliant resource and reserve estimates for the Cobre Panama Deposits at 5 March, 2012 (Inmet Mining website, 2012) were:
Measured + indicated resoures - 4.167 Gt @ 0.35% Cu, 0.07 g/t Au, 1.30 g/t Ag. 0.006% Mo;
Inferred resoures - 3.749 Gt @ 0.23% Cu, 0.04 g/t Au, 1.0 g/t Ag, 0.004% Mo;
Proven + probable reserves (included in resources) - 2.319 Gt @ 0.40% Cu, 0.07 g/t Au, 1.4 g/t Ag, 0.007% Mo.
Published NI 43-101 compliant resource and reserve estimates for the Molejón Project at 1 January, 2011 (Petaqiulla Minerals website, 2012) at a cut-off of 0.20 g/t Au were:
Measured + indicated resoures - 31.586 Mt @ 0.80 g/t Au, 1.74 g/t Ag (for 26.385 t of Au);
Inferred resoures - 3.33 Mt @ 0.35 g/t Au, 1.4 g/t Ag
Proven + probable reserves - 15.33 Mt @ 1.305 g/t Au, 2.05 g/t Ag.
Published NI 43-101 compliant resource and reserve estimates for the Cobre Panama Deposits - Botija, Colina, Medio, Valle Grande, Balboa, Botija Abajo and Brazo at 31 December, 2018 (First Quantum, 2020) at a cut-off of 0.15 g/t Au were:
Measured + indicated resoures - 3.587 Gt @ 0.37% Cu, 0.07 g/t Au, 0.006 % Mo, 1.33 g/t Ag;
Inferred resoures - 1.050 Gt @ 0.26% Cu, 0.04 g/t Au, 0.005 % Mo, 1.08 g/t Ag;
Proven + probable reserves - 3.143.7 Gt @ 0.38% Cu, 0.07 g/t Au, 59.3 ppm Mo, 1.37 g/t Ag.
NOTE: Mineral Resources are inclusive of Ore Reserves.
The information in this summary is largely sourced from: Rose, W.E., Davis, B., Sim, R., Burge, C., Kozak, A. and Wells, G.S., 2010, Mina de Cobre Panama Project, Panama, a NI 43-101 Technical Report prepared by INMET Mining Corporation, 188p.
The most recent source geological information used to prepare this summary was dated: 2010.
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.
Mina de Cobre area
Sepp, M.D. and Dilles, J.H., 2018 - Structural Evolution, Vein Orientation, and Paragenesis of the Botija Porphyry Cu-Mo-(Au) Deposit, Panama: in Econ. Geol. v.113, pp. 857-890.|
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