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Item type:Publication, Trace element geochemistry of sphalerite and chalcopyrite in arc-hosted VMS deposits(Elsevier, 2021-08-26)Trace element compositions of sphalerite and chalcopyrite have been investigated for four arc-hosted Cretaceous VMS deposits (María Teresa, Perubar, and Palma in Peru, and Cerro de Maimón in the Dominican Republic) using laser ablation inductively-coupled plasma mass spectrometry. In sphalerite, Fe, Mn, Cd, Hg, Ag, Sb, Se, In, Ge, and Ga are lattice-bound, whereas Sn, Tl, Bi, and Pb occur at least partly as mineral microinclusions. Significant variations in the contents of minor and trace elements are observed in sphalerite grains from individual deposits. A strong negative correlation between Fe (Inter-Quartile Range [IQR] 44,009–18,168 ppm) and Zn indicates a dominant Fe2+ ↔ Zn2+ simple isovalent substitution. Regarding potential high-tech by-products, the contents of In (IQR 42–1.6 ppm, up to 415 ppm) and Ga (IQR 31–5.9 ppm, up to 96 ppm) in the studied sphalerite are normally much higher than those of Ge (IQR 0.85–0.16 ppm, up to 9.3 ppm). Correlation trends suggest Cu+ + In3+ ↔ 2Zn2+, Cu+ + Ga3+ ↔ 2Zn2+, and more complex substitution mechanisms of Zn involving combinations of monovalent (Cu+, Ag+), divalent (Ge2+?), trivalent (In3+, Ga3+, [Sn3+?]), and quadrivalent (Ge4+, Sn4+) cations. As for chalcopyrite, Zn, Ag, Sn, Cd, Se, In, Ga, and Ge are interpreted to be lattice-bound, whereas Mo, Au, Tl, Sb, Pb, and Bi probably occur as microinclusions. Relative to sphalerite, chalcopyrite is depleted in In (IQR 28–8.4 ppm, up to 49 ppm) and Ga (IQR 8.3–2.9 ppm, up to 24 ppm) and enriched in Ge (IQR 5.9–0.70 ppm, up to 80 ppm). Of the other trace elements, Zn (IQR 426–190 ppm) is the most highly concentrated in the studied chalcopyrite, followed by Ag (IQR 136–23 ppm), Se (IQR 64–22 ppm), Sn (IQR 53–1.3 ppm), and Cd (IQR 12–6.0 ppm). General positive correlation trends between Zn, Cd, In, Ge, and Ga in chalcopyrite suggest varied coupled substitution mechanisms of Fe and Cu with fluctuating valences due to covalent bonding. Trace-element distribution patterns in sphalerite and chalcopyrite were studied for the zone-refined Sofía-D massive sulfide body in the María Teresa deposit, which comprises a lower lower portion of dominant pyrite sheathed upward by zones of chalcopyrite (Cu zone), sphalerite (Zn zone) and galena + sphalerite ± fahlore ± barite (Pb – Zn – Ag zone). Bottom to top of the sulfide body, sphalerite records progressive depletion in In, Cu, Mn, and Se, and enrichment in Ge. This distribution pattern agrees with increasing crystallization temperatures and/or volatile magmatic influx towards the lower portion of the massive mineralization. Distribution of trace elements in chalcopyrite is rather uneven except for a sustained enrichment in Se towards the basal portion of the sulfide body. The fact that such trends are preserved in spite of extensive recrystallization during thermal metamorphism in parts of the Sofía-D massive sulfide mineralization suggests i) a closed metamorphic system and ii) that element interdiffusion was prominently local. Accordingly, we propose that sphalerite lattice-bound trace elements distribution patterns described in this article can help determine the polarity of massive sulfide bodies in VMS districts in metamorphosed and tectonized terranes. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Distribution of indium, germanium, gallium and other minor and trace elements in polymetallic ores from a porphyry system: the Morococha district, Peru(Elsevier, 2021-09-01)We report indium, germanium, gallium, and other minor and trace elements contents in sphalerite, chalcopyrite, galena, and tetrahedrite-tennantite occurring in skarn and skarn-free (“Cordilleran”) polymetallic mantos and vein ore bodies in the Miocene porphyry-related Morococha District, Central Peru. Among the investigated minerals, LA-ICP-MS measurements indicate that In and Ga concentrate mostly in sphalerite (Inter-Quartile Range [IQR] 217–2.7 ppm and up to 4608 ppm In; IQR 61–2.0 ppm and up to 2137 ppm Ga) and chalcopyrite (IQR 109–32 ppm and up to 1070 ppm In; IQR 62–1.5 ppm and up to 630 ppm Ga). In coeval generations of sphalerite and chalcopyrite, the contents of In and Ga in sphalerite are at least two times higher than in chalcopyrite. Germanium content is generally low in the four analyzed minerals (IQR 1.2–0.19 ppm), although late Fe-poor sphalerite may yield much higher values (IQR 129–74 ppm). Certain trace element contents appear to correlate with (i) the evolving characteristics of the hydrothermal fluids during individual mineralization events, and (ii) the location of the studied ore bodies relative to the hydrothermal feeders. The highest In values in sphalerite are found in high-sulfidation assemblages in Cordilleran polymetallic veins and, with lower amounts, in low-sulfidation assemblages in skarn bodies. In intermediate-sulfidation assemblages in Cordilleran mineralization, In content decreases from early to late generations of sphalerite, while that of Ge increases. Spatial trace-element trends in Cordilleran veins and replacement bodies formed during the so-called “Morococha district-scale polymetallic event” include, from porphyry-distal to porphyry-proximal locations: i) In and Cu, and to a lesser extent Ga, enrichment in sphalerite; ii) Se and Hg enrichment and Sn and Ag depletion in chalcopyrite; iii) In enrichment in galena; and iv) Ag depletion in tetrahedrite-tennantite. Our dataset suggests that In is incorporated in the sphalerite crystal lattice via coupled substitutions involving Cu and subordinately also Sn and Ag. Availability of Cu in the mineralizing fluids is therefore key to In enrichment in sphalerite. Progressive dilution of metal-rich magmatic-hydrothermal fluids and Cu precipitation probably account for the progressive In depletion in distal-to-porphyry Zn-Pb-Ag and Ag-Pb Cordilleran polymetallic mineralization and in late sphalerite generations in intermediate-sulfidation assemblages. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Geology, mineralogy, and cassiterite geochronology of the Ayawilca Zn-Pb-Ag-In-Sn-Cu deposit, Pasco, Peru(Springer Science+Business Media, 2021-09-13)The Ayawilca deposit in Pasco, Peru, represents the most significant recent base-metal discovery in the central Andes and one of the largest undeveloped In resources globally. As of 2018, it hosts an 11.7 Mt indicated resource grading 6.9% Zn, 0.16% Pb, 15 g/t Ag, and 84 g/t In, an additional 45.0 Mt inferred resource grading 5.6% Zn, 0.23% Pb, 17 g/t Ag, and 67 g/t In, and a separate Sn-Cu-Ag inferred resource of 14.5 Mt grading 0.63% Sn, 0.21% Cu, and 18 g/t Ag. Newly obtained U–Pb dates for cassiterite by LA-ICP-MS (22.77 ± 0.41 and 23.05 ± 2.06 Ma) assign the Ayawilca deposit to the Miocene polymetallic belt of central Peru. The polymetallic mineralization occurs as up to 70-m-thick mantos hosted by carbonate rocks of the Late Triassic to Early Jurassic Pucará Group, and subordinately, as steeply dipping veins hosted by rocks of the Pucará Group and overlying Cretaceous sandstones-siltstones of the Goyllarisquizga Group. Relicts of a distal retrograde magnesian skarn and cassiterite (stage pre-A) were identified in the deepest mantos. The volumetrically most important mineralization at Ayawilca comprises a low-sulfidation assemblage (stage A) with quartz, pyrrhotite, arsenopyrite, chalcopyrite, Fe-rich sphalerite, and traces of stannite and herzenbergite. Stage A sphalerite records progressive Fe depletion, from 33 to 10 mol% FeS, which is compatible with the observed transition from low- to a subsequent intermediate-sulfidation stage (B) marked by the crystallization of abundant pyrite and marcasite. Finally, during a later intermediate-sulfidation stage (C) sphalerite (up to 11 mol% FeS), galena, native bismuth, Cu-Pb-Ag sulfosalts, siderite, Mn-Fe carbonates, kaolinite, dickite, and sericite were deposited. This paragenetic evolution shows striking similarities with that at the Cerro de Pasco Cordilleran-type polymetallic deposit, even if at Ayawilca stage C did not reach high-sulfidation conditions. The occurrence of an early retrograde skarn assemblage suggests that the manto bodies at Ayawilca formed at the transition between distal skarn and skarn-free (Cordilleran-type) carbonate-replacement mineralization. Mineral assemblages define a T-fS2 evolutionary path close to the pyrrhotite-pyrite boundary. Buffering of hydrothermal fluids by underlying Devonian carbonaceous phyllites of the Excelsior Group imposed highly reduced conditions during stage A mineralization (logfO2 < − 30 atm). The low fO2 favored efficient Sn mobility during stages pre-A and A, in contrast to other known ore deposits in the polymetallic belt of central Peru, in which the occurrence of Sn minerals is minor. Subsequent cooling, progressive sealing of vein walls, and decreasing buffering potential of the host rocks promoted the shift from low- (stage A) to intermediate-sulfidation (stages B and C) states. LA-ICP-MS analyses reveal significant In contents in Fe-rich sphalerite (up to 1.7 wt%), stannite (up to 1908 ppm), and chalcopyrite (up to 1185 ppm). The highest In content was found in stage A sphalerite that precipitated along with chalcopyrite and stannite, thus pointing to the early, low-sulfidation assemblage as prospective for this high-tech metal in similar mineral systems. Indium was likely incorporated into the sphalerite crystal lattice via Cu+ + In3+ ↔ 2 Zn2+ and (Sn, Ge)4+ + (Ga, In)3+ + (Cu + Ag)+ ↔ 4 Zn2+ coupled substitutions. Indium incorporation mechanisms into the stannite and chalcopyrite crystal lattices remain unclear. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Genesis of the exotic chrysocolla — “copper pitch/wad” — atacamite/brochantite ore at the Exótica (Mina Sur) deposit, Chuquicamata, Chile(Springer Science+Business Media, 2022-11-09)Detailed mineralogical and textural studies, combined with sequential X-ray diffraction and geochemical modeling, helped to solve the “copper pitch/wad” enigma in the Exótica deposit located downstream of the Chuquicamata porphyry copper deposit. Copper pitch and copper wad are essentially chrysocolla with co-precipitated Mn oxides, mainly birnessite, as well as pseudo-amorphous Mn oxide/oxyhydroxides. Linking the mineralogical, geochemical, and textural evidences with the geological, tectonic, and climatic evolution of the Chuquicamata–Calama area, a four-step genetic model for the evolution of the Exótica deposit is presented: (A) formation of a mature supergene enrichment profile at Chuquicamata (~ 30–25 Ma to ~ 15 Ma) during an erosion-dominated regime (∼900 m of erosion) which was accompanied by acidic (pH ∼2–4) Cu-Mn-Si-dominated rock drainage (ARD) with fluid flow southwards through the Exótica valley towards the Calama Basin, resulting in a strongly kaolinized and chrysocolla/copper wad-impregnated bedrock of the Exótica deposit; (B) deposition of the Fortuna gravels in the Exótica valley (starting ∼19 Ma) intercepted the Cu-Mn-Si-dominated ARD, triggering the main chrysocolla, copper pitch/wad mineralization as syn-sedimentary mineralization by chiefly surficial flow in strongly altered gravels; (C) tectonic freezing and onset of hyper-aridity (∼15–11 Ma) exposed the enriched chalcocite blanket of Chuquicamata to oxidation, resulting in acidic (pH ~ 2–4) and Cu-Si-dominated solutions with less Mn. These solutions percolated in a slightly more reducing groundwater flow path and mineralized relatively unaltered gravels with pure chrysocolla; and (D) ingression of confined chloride-rich groundwater in the upper oxidation zone of Chuquicamata, most likely between 6 and 3 Ma, is responsible for the atacamite/brochantite mineralization (pH ~ 5.5–7) of mainly unaltered gravels in the northern and central part of the Exótica deposit. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Neoformation of exotic copper minerals from gel-like precursors at the Exótica deposit, Chuquicamata, Chile(Springer Science+Business Media, 2022-11-16)At the Exótica deposit, south of the giant porphyry copper deposit of Chuquicamata (Atacama Desert, Chile), Cu-rich groundwater seeped out at several locations in the Exótica open pit (Mina Sur) during sampling in 2009–2011. At their outflows, these solutions formed blueish and greenish copper-bearing gel-like precipitates. These gels contained atacamite and copper sulfate hydroxides such as devilline, spangolite, posnjakite, schulenbergite, and brochantite, which were identified by XRD, SEM, ESEM, and FTIR. The formation of the gel materials was studied under humid and dry conditions during and after maturation and water evaporation. Atacamite was found associated to outflowing saline solutions with pH 5.7, SO4/Cl weight ratios of 0.42–0.48, SO4/NO3 ratios of 0.48–0.50. These solutions are seen as an expression of the the lower aquifer of the Calama basin. Most copper sulfate hydroxides (spangolite, posnjakite, schulenbergite) were associated with slightly acidic freshwaters (pH 6.0 to 6.5, SO4/Cl ratios of 3.08–4.99, SO4/NO3 ratios of 2.52–3.13). In contrast, devilline formed in gels with near neutral to slightly alkaline water (pH 7.2 to 7.8, SO4/Cl ratio of 8.34, and SO4/NO3 ratio of 6.05). Non-copper-bearing precipitates formed by evaporation of the supernatant solutions from the gel. Gypsum precipitated first, then blödite (sodium-magnesium sulfate), and finally halite. Slightly negative sulfur isotope values suggest that the sulfur source in the neoformed gels is primarily the oxidation of sulfides rather than sulfate of sedimentary origin. The studied copper-gel seeps suggest that they might represent a modern precursor of the latest atacamite-brochantite-gypsum mineralization event at Exótica. These data support that the atacamite-brochantite-gypsum mineralization at Exótica is linked to the inflow of Cl-SO4-dominated groundwater from the lower saline aquifer of the Calama basin into the Chuquicamata-Exótica-Radomiro Tomic complex. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Sedimentary Evolution of a Late Triassic Salt Giant and a Synchronous Carbonate Unit Between the Peruvian Andean Cordillera and the Brazilian Amazonian Foreland(American Association of Petroleum Geologists, 2023-01-01)Salt giants with mixed evaporites/carbonates are sedimentary systems poorly understood in terms of sequence stratigraphy, tectonic control, and related natural resources. To improve the knowledge of these systems, a sedimentology study of a Late Triassic salt giant between the Subandean fold-thrust belt (SFTB) of Peru and the Brazilian Amazonian foreland (AF) was performed on the pre- to postsalt deposits using field observations, thin-section descriptions, and well-log analysis. In addition, this study was compared with sedimentary observations of Upper Triassic carbonate successions from the Subandean-Cordillera transition zone (SCTZ) documented in previous works. This resulted in the following sedimentary events associated to a relative sealevel fluctuation: first transgression, regression, and second transgression. In the SFTB and AF, during the first transgression, continental/transitional siliciclastic environments with sporadic marine incursions allowing the development of salt ponds were formed first. Subsequently, a salt basin surrounded by a mudflat was established. At the end of the first transgression, carbonate deposits dominated. During the subsequent regression, a sulfate platform was established followed by a salt basin enveloped by mudflats and exposed areas. This regression terminated with the development of a central mudflat and an increase of the exposed areas. In the second transgression, carbonates and an eastward mudflat with gypsum ponds dominated the sedimentation. In the SCTZ, external-platform to deep-basin carbonates dominated the sedimentation during the three events. Based on this evolution, eustatic oscillations of the global oceanic level, and structural features published in previous works, it is interpreted that the deposition of the studied salt giant and external carbonates were controlled by thermal sagging and eustatic sea-level oscillations. The available data suggest the existence of a westward migration of the subsidence from the Norian (mid Late Triassic) to the Triassic-Jurassic boundary that may be caused by slab steepening. Hydrocarbon reservoirs and stratabound, sediment-hosted Cu-Ag and Zn-Pb ore deposit occurrences are also partly controlled by the evolution of the mixed evaporite/carbonate sedimentary system in the region between the SCTZ and the AF. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Germanium- and Gallium-Rich Sphalerite in Mississippi Valley–Type Deposits: The San Vicente District and the Shalipayco Deposit, Peru(Springer Science and Business Media Deutschland GmbH, 2023-06-01)Sphalerite in Mississippi Valley–type (MVT) deposits hosts significant resources of both germanium and gallium. Here, we provide a survey on the distribution of Ge, Ga, and other minor and trace elements in sphalerite from MVT deposits in the Eastern Cordillera and sub-Andean regions of Peru, including the San Vicente deposit and the nearby Chilpes and Huacrash prospects, and the Shalipayco deposit. We present also a micro- and nano-scale textural characterization of Ge-rich sphalerite. In situ laser ablation-inductively coupled plasma-mass spectrometry analyses yielded Ge contents (inter-quartile range [IQR] = 164–36 ppm for the San Vicente district and IQR = 425–101 ppm for the Shalipayco deposit) that overlap with the range reported for sphalerite from other MVT deposits elsewhere. The highest Ge contents (IQR = 1207–375 ppm, up to 1861 ppm) were found in Fe-poor orange sphalerite deposited during a volumetrically minor second mineralization step in the San Vicente deposit located mainly in steep veins that crosscut the main first-step mineralization dominated by darker sphalerite. Reddish-brown sphalerite from Chilpes (IQR = 445–22 ppm, up to 1745 ppm) and brownish orange sphalerite from Huacrash (IQR = 650–34 ppm, up to 855 ppm) also yielded remarkably high Ge values. In Shalipayco, the highest Ge contents were analyzed in late Fe-poor yellow sphalerite (IQR = 375–267 ppm, up to 1119 ppm). The highest Ga contents were determined in reddish-brown sphalerite from the Chilpes prospect (IQR = 1156–0.26 ppm, up to 3943 ppm), although Ga contents are, in general, much lower than those of Ge in most analyzed sphalerite (IQR = 27–0.22 ppm in the San Vicente district and IQR = 2.8–0.081 ppm in the Shalipayco deposit). These figures place some of the analyzed sphalerite types among the Ge- and Ga-richest samples ever reported. Linkage of textural and compositional data points to light-colored, chiefly orange and yellow sphalerite generations crystallizing at lower temperatures and relatively late in the paragenetic sequences as those with the highest Ge contents. In contrast, the paragenetic control on Ga enrichment is unclear. Focused ion beam and high-resolution transmission electron microscopy (FIB-HRTEM) investigation combined with trace element content correlations reveal selective partitioning of Ge and Ga into sphalerite as structurally bound elements and their incorporation via substitution mostly coupled to monovalent cations triggering polytypism.