Carboniferous Orogenic Gold Deposits at Pataz, Eastern AndeanCordillera, Peru: Geological and Structural Framework, Paragenesis, Alteration,and 40Ar/39Ar Geochronology (original) (raw)
Mineralium Deposita, 2014
Mineral de Talca is a rare occurrence of Mesozoic, gold-bearing quartz vein mineralisation situated within the Coastal Range of northern Chile. Quartz veins controlled by NNW-SSE-trending faults are hosted by Devonian-Carboniferous metasediments of greenschist facies and younger, undeformed granitoid and gabbro intrusions. The principal structural control in the area is the easterly dipping, NNW-SSE-trending El Teniente Fault, which most likely developed as an extensional normal fault in the Triassic but was later reactivated as a strike-slip fault during subsequent compression. A dilational zone in the El Teniente Fault appears to have focussed fluid flow, and an array of NW-SE-trending veins is present as splays off the El Teniente Fault. Mineralised quartz veins typically up to a metre thick occur in three main orientations: (1) parallel to and within NNW-SSE-trending, E-dipping faults throughout the area; (2) along NW-SE-trending, NEdipping structures which may also host andesite dykes; and (3) rarer E-W-trending, subvertical veins. All mineralised quartz veins show evidence of multiple fluid events with anastomosing and crosscutting veins and veinlets, some of which contain up to 3.5 vol.% base metal sulphides. Mineralogically, Au is present in three textural occurrences, identified by 3D CT scanning: (1) with arsenopyrite and pyrite in altered wall rock and along the margins of some of the veins; (2) with Cu-Pb-Zn sulphides within quartz veins; and (3) as nuggets and clusters of native Au within quartz. Fluid inclusion work indicates the presence of CO 2 -CH 4 -bearing fluids with homogenisation temperatures of ∼350°C and aqueous fluids with lowmoderate salinities (0.4-15.5 wt% NaCl eq.) with homogenisation temperatures in the range of 161-321°C. The presence of Au with arsenopyrite and pyrite in structurally controlled quartz veins and in greenschist facies rocks with evidence of CO 2 -bearing fluids is consistent with an orogenic style classification for the mineralisation. However, the significant amounts of base metals and the moderate salinity of some of the fluids and the proximity to felsic granitoid intrusions have raised the possibility of an intrusion-related origin for the mineralisation. Vein sulphides display S isotope signatures (δ 34 S +2.1 to +4.3‰) that are intermediate between the host rock metasediments (δ 34 S +5.3 to +7.5‰) and the local granitoids (δ 34 S +1.3 to +1.4‰), indicating a distinct crustal source of some of the S in the veins and possibly a mixed magmaticcrustal S source. The local granite and granodiorite give U-Pb zircon ages of 219.6±1 and 221.3±2.8 Ma, respectively. Lead isotopic compositions of galena in the veins are consistent, Editorial handling: D. Craw and B. Lehmann Electronic supplementary material The online version of this article (suggesting derivation from a homogeneous source. Differences, however, between the isotopic signatures of the veins and igneous feldspars from nearby intrusions imply that these bodies were not the source of the metals though an igneous source from depth cannot be discounted. The Triassic age of the granitoids is consistent with emplacement during regional crustal extension, with the El Teniente Fault formed as an easterly dipping normal fault. The change to a compressional regime in the mid-Jurassic caused reactivation of the El Teniente Fault as a strike-slip fault and provided a structural setting suitable for orogenic style mineralisation. The intrusions may, however, have provided a structural competency contrast that focused the mineralising fluids in a dilational jog along the El Teniente Fault to form WNW-trending veins. As such, the mineralisation is classified as orogenic style, and the identification of the key mineralogical, isotopic and structural features has implications for exploration and the development of similar deposits along the Coastal Range.
Ore Geology Reviews, 2008
The high-sulfidation system of Cerro Millo is hosted in a Late Miocene andesitic paleo-stratovolcano in the High Andes of southern Peru. Very pronounced advanced-argillic (alunite), silicic, and argillic (kaolinite and smectite) alteration characterizes the central part of the hydrothermal system. Propylitic alteration is developed in a 3 to 4 km wide outer halo. Abundant alunite occurs as hypogene, acicular crystals, and very fine-grained aggregates; the latter formed during near-surface steam-heated overprinting. Hypogene alunite has an Ar-Ar plateau age of 10.8 ± 0.9 Ma (2σ), and is synchronous with the andesitic volcanism (Ar-Ar on biotite: 11.0 ± 0.5 Ma). A second ill-defined alunite age plateau of 8.0 ± 0.9 Ma is probably related to steam-heated overprint and points to major erosion in between both hydrothermal events. Telescoping is also evident by a series of silicified horizons which mark the paleo-groundwater table. These units have elevated mercury, antimony and arsenic levels. Late-phase barite occurs in some structurally controlled advanced-argillic altered envelopes. The hypogene alteration mineralogy points to temperatures at ≤250°C. Hydraulic fracturing and steamheated overprinting suggest a shallow boiling environment. Slight gold enrichment is observed in the lowermost exposed parts of the system.
Evolution of calc-alkaline volcanism and associated hydrothermal gold deposits at Yanacocha, Peru
2010
Clusters of high-sulfidation epithermal deposits containing more than 50 Moz of gold are hosted by advanced argillic-altered Miocene volcanic rocks in the Yanacocha district, northern Peru (lat. 6°59'30" S, long. 78°30'45" W). We describe the nature of the volcanism and its relation to the gold ores on the basis of new district-scale geologic mapping, 69 40 Ar/ 39 Ar ages on igneous rocks and hydrothermal alunite, and petrologic and geochemical investigations. Volcanic rocks of the Calipuy Group are the oldest Cenozoic rocks at Yanacocha, and include the Huambo Cancha andesite, andesitic lahars of Tual and Chaupiloma (19.5-15.9 Ma), and the dacitic Cerro Fraile pyroclastics (15.5-15.1 Ma). The younger Yanacocha Volcanics (14.5-8.4 Ma) form a cogenetic series of lavas and pyroclastic rocks with a cumulative volume of ~88 km 3 that represents eruption from a moderate-size volcanic center. Early pyroxene>hornblende-bearing lavas of the Atazaico Andesite (14.5-13.3 Ma) erupted from small stratovolcanoes progressively younger from southwest to northeast. Dacitic dikes followed that are spatially associated with gold deposits at Quilish and Cerro Negro (~7 Moz Au) and stage 1 alunite (13.6-12.6 Ma). The Colorado Pyroclastics erupted in the center of the district and include the hornblende-and biotite-bearing andesitic to dacitic Cori Coshpa (12.6 Ma) and Maqui Maqui (12.5-12.4 Ma) ignimbrites. The Colorado Pyroclastics are overlain by hornblende>pyroxene-bearing andesitic to dacitic lavas, flow-domes, and minor pyroclastic rocks of the Azufre Andesite (12.1-11.6 Ma). Widespread stage 2 alunite (11.5 Ma) and minor gold deposition (~0.5 Moz) closely follow. The San Jose Ignimbrite (11.5-11.2 Ma) overlies the Azufre Andesite and stage 2 alunite and includes three members of hornblende-pyroxene (biotite) dacite and andesite that erupted in the center of the district and flowed southward. Mineralogically similar domes were emplaced into the inferred vents. The Coriwachay Dacite (10.8-8.4 Ma) forms the youngest and most silica rich igneous rocks in the district, and includes intrusions and flow domes of dacite to rhyolite at Corimayo (10.8 Ma), Cerro Yanacocha (9.9 Ma), and Yanacocha Lake (8.4 Ma). Most of the gold (>47 Moz) was deposited at Yanacocha during intrusion of the late Coriwachay Dacite. These late dacites are volumetrically smallest (~2% of the total volume of erupted magma) and are temporally associated with stage 3 to 5 alunites. Stage 3 alunite (11.0-10.7 Ma) developed along a northeast trend for 9 km that includes the gold deposits of Corimayo, San Jose, Carachugo, and Maqui Maqui. The deeper Kupfertal Cu-Au porphyry has an age of 10.7 Ma on hydrothermal biotite and underlies zones of stage 4 and 5 quartz-alunite alternation that are 0.8 and 1.5 m.y. younger, respectively. Stage 4 alunite ranges in age from 10.2 to 10.3 Ma at the Tapado and Chaquicocha Sur gold deposits to Cerro Sugares east of the Maqui Maqui deposit. Stage 4 also includes a younger alunite age of 9.9 Ma from the San Jose gold deposit. Stage 5 alunite ranges from ~9.3 to ~8.2 Ma at Cerro Yanacocha, the largest gold deposit in the district. All these deposits contain massive and vuggy quartz, quartz-alunite, and quartz-pyrophyllite alteration associated with pyrite±enargite-tennantite-covellite. Magmatism in the Yanacocha district lasted for ~11 m.y. The Yanacocha Volcanics spanned the last ~6 m.y. of this period and were associated with long-lived magmatic-hydrothermal activity and episodic gold mineralization. The Yanacocha calc-alkaline suite was oxidized, water and sulfate rich, and evolved from early pyrox-ene>hornblende andesite to late titanite-bearing dacite and minor rhyolite. Several dacites contain populations of both high-and low-aluminum hornblendes that crystallized in the middle and upper crust, respectively. The variation of Mg, Ti, P, Sr, and Ba contents in these rocks is consistent with a complex magmatic origin via both cooling, fractional crystallization, periodic recharge of deeply derived hydrous basaltic or andesitic melts, and mixing with silicic melts derived by crustal melting. Low eruption rates, high phenocryst contents of the volcanic rocks, and widespread hydrothermal alteration are consistent with the hypothesis that most of the magmas at Yanacocha crystallized in shallow chambers as granitoids that passively degassed ore fluids. The compositional diversity of the volcanic rocks together with an extended magmatic-hydrothermal history reflect complex magmatic processes that were optimum for producing the world-class gold deposits at Yanacocha.
Mineralium Deposita, 2001
The Tapajo s region is one domain of a major Paleoproterozoic orogenic belt, named Tapajo s±Parima and is discussed in the context of the evolution of the Amazon Craton. The orogenic belt is composed of a back-arc sequence, four volcano-plutonic arcs, intra-arc sedimentation and is limited to the east by the cratonic rocks of the Central Amazon Province. The evolution and timing of the main events is established by zircon, baddeleyite, and titanite SHRIMP U±Pb geochronology of 29 rock samples, while lead and argon isotopes are used to study the age and source of the gold mineralization. Based on the mesoscopic nature of the orebodies, and, in some cases, on microthermometric and stable isotope data, the Tapajo s gold deposits are classi®ed as (1) orogenic and (2) intrusion-related, and may be grouped into four deposit-type categories: (1) orogenic, turbidite-hosted: disseminated and quartz±pyrite veinlet deposits, hosted by metaturbidites (lower greenschistfacies, Jacareacanga Group) and emplaced in ductile structures; (2) orogenic, magmatic arc-hosted: disseminated and pyrite±quartz±carbonate vein deposits, hosted by metamorphic rocks (CuiuÂ-Cuiu Complex) and formed under a ductile±brittle regime, with the Ouro Roxo deposit as a type example; (3) intrusion-related, epizonal quartz-vein deposits: vertical to subvertical quartz-pyrite veins and pyrite disseminations ®lling extensional brittle faults; and (4) intrusion-related, epizonal, disseminated/ stockwork deposits, the type-example being the Serrinha deposit. Gold mineralization of type 3 is similar to that of Korean-type, while type 4 mineralization shows some similarities to porphyry-type deposits. Galena Pb±Pb and muscovite Ar±Ar data indicate an age of 1,860 Ma for the intrusion-related gold mineralization. Preliminary Pb isotope data on K-feldspar indicate that thē uid source was more likely to have been from within the Jacareacanga, CuiuÂ-Cuiu and Tropas units than the CreporizaÄ o, Maloquinha, and Iriri units. This study shows the existence of two main types (orogenic and intrusion-related) of gold deposits, which are related to speci®c tectono-magmatic events that occurred during a limited period of time in the orogenic belt evolution. This information may be useful as a guide for gold exploration along the orogenic belt.
Mineralium Deposita, 2009
New U–Pb, Re–Os, and 40Ar/39Ar dates are presented for magmatic and hydrothermal mineral phases in skarn- and porphyry-related ores from the Nambija and Pangui districts of the Subandean zone, southeastern Ecuador. Nambija has been one of the main gold-producing centers of Ecuador since the 1980s due to exceptionally high-grade ores (average 15 g/t, but frequently up to 300 g/t Au). Pangui is a recently discovered porphyry Cu–Mo district. The geology of the Subandean zone in southeastern Ecuador is dominated by the I-type, subduction-related, Jurassic Zamora batholith, which intrudes Triassic volcanosedimentary rocks. The Zamora batholith is in turn cut by porphyritic stocks, which are commonly associated with skarn formation and/or porphyry-style mineralization. High precision U–Pb and Re–Os ages for porphyritic stocks (U–Pb, zircon), associated prograde skarn (U–Pb, hydrothermal titanite), and retrograde stage skarn (Re–Os, molybdenite from veins postdating gold deposition) of the Nambija district are all indistinguishable from each other within error (145 Ma) and indicate a Late Jurassic age for the gold mineralization. Previously, gold mineralization at Nambija was considered to be Early Tertiary based on K–Ar ages obtained on various hydrothermal minerals. The new Jurassic age for the Nambija district is slightly younger than the 40Ar/39Ar and Re–Os ages for magmatic–hydrothermal minerals from the Pangui district, which range between 157 and 152 Ma. Mineralization at Nambija and Pangui is associated with porphyritic stocks that represent the last known episodes of a long-lived Jurassic arc magmatism (∼190 to 145 Ma). A Jurassic age for mineralization at Nambija and Pangui suggests that the Northern Andean Jurassic metallogenic belt, which starts in Colombia at 3° N, extends down to 5° S in Ecuador. It also adds a new mineralization style (Au-skarn) to the metal endowment of this belt.
Ore Geology Reviews, 2008
Epigenetic gold mineralization occurs in the Marmato mining district, within the Calima Terrain of the Setentrional Andes, Colombia. Regional rocks associated with this mineralization include: graphite-and chlorite-schists of the Arquia Complex; metamorphosed during the Cretaceous, Miocene sandstones, shales and conglomerates of the Amagá Formation; as well as pyroclastic rocks (clasts of basalt, andesites and mafic lavas) and subvolcanic andesitic/dacitic bodies of the Combia Formation (9 to 6 Ma). The subvolcanic Marmato stock hosts mesothermal and epithermal low-sulfidation Au-Ag ores in the form of distensional veins, stockwork, and quartz veinlets within brecciated zones. Ore minerals are pyrite, sphalerite and galena with subordinate chalcopyrite, arsenopyrite, pyrrhotite, argentite and native gold/electrum. Sericitized plagioclase from a porphyry dacite yielded a K-Ar age of 5.6± 0.6 Ma, interpreted as the age of ore deposition. This is in close agreement with the age of reactivation of the Cauca-Romeral Fault System (5.6 ± 0.4 Ma), which bounds the Calima Terrain. A porphyry andesite-dacite (6.7 ± 0.1 Ma), hosting the Au-Ag veins, shows a measured 87 Sr/ 86 Sr between 0.70440 and 0.70460, ε Nd between +2.
Mineralogy and Petrology, 2008
The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous andesites of the Los Elquinos Formation at La Serena (≈29º47´S Lat., 70º43'W Long., Chile). Quartz-sulfide veins of economic potential are hosted by N25W and N20E fault structures associated with quartz-illite alteration (+supergene kaolinite). The main ore minerals in the deposit are pyrite, chalcopyrite ± fahlore (As/(As+Sb): 0.06 -0.98), with electrum, sphalerite, galena, bournonite-seligmanite (As/(As+Sb): 0.21 -0.31), marcasite, pyrrhotite being accessory phases. Electrum, with an Ag content between 32 and 37 at. %, occurs interstitial to pyrite aggregates or along pyrite fractures. Pyrite commonly exhibits chemical zonation with some zones up to 1.96 at. % As. Electron probe microanalyses of pyrite indicate that As-rich zones do not exhibit detectable Au values. Fluid inclusion microthermometry shows homogenization temperatures between 130 and 352 ºC and salinities between 1.6 and 6.9 wt. % NaCl eq. Isotope data in quartz, ankerite and phyllosilicates and estimated temperatures show that δ 18 O and δD for the hydrothermal fluids were between 3 and 10‰ and between -95 and -75‰, respectively. These results suggest the mineralizing fluids were a mixture of meteoric and magmatic waters. An epithermal intermediate-sulfidation model is proposed for the formation of El Dorado deposit. from the Miocene-Pleistocene represent higher reserves of gold and copper than older deposits (e.g., . This paper presents the results of the first study of the mineralogy and mineral chemistry (XRD, SEM and EMPA), fluid inclusion microthermometry and stable isotope geochemistry of the El Dorado Cu-Au deposit. The deposit occurs within pervasively hydrothermally altered volcanic rocks of Upper Cretaceous age in the Precordillera of central-north Chile, at ≈29º47' Lat. S 70º43'W Long. (Fig. ). We discuss the genesis of this deposit within the Late Cretaceous -Paleogene geodynamic evolution of this segment of the Coastal Range and Precordillera, and we present a classification of the deposit. Our study focuses on the ore mineralogy and mineral chemistry, with emphasis on precious metal (Au and Ag) and related minerals (i.e., pyrite contents and their occurrence). This is providing the foundation for the further geochemical and mineralogical investigations. In the Coastal Range and Precordillera of the La Serena area, along the Elqui Valley, a complete Cretaceous to Tertiary volcano-sedimentary sequence is present (Fig. ). The Lower Cretaceous rocks are included in the Arqueros and Quebrada Marquesa Formations, while the Upper Cretaceous volcaniclastic rocks are represented by the upper part of Viñita and Los Elquinos Formations Pineda and Emparan, 1997; Emparan and Pineda, 1999). A change in the depositional conditions from shallow-water marine basins in the Lower Cretaceous to continental in the Upper Cretaceous sedimentary sequences has been proposed by Pineda and Emparan (1997). Only limited geochronological data are available for basaltic lavas belonging to the Viñita Formation; a K-Ar age of 82±3 Ma (whole-rock, Pineda and Emparan, 1997) must be interpreted as a minimum age due to alteration, rather than the age of lava extrusion (Fig. ), while zircon U-Pb ages of 84.8±0.3 Ma and 84.6±0.2 Ma were obtained from stratigraphically higher rhyodacites of this formation (Emparan and Pineda, 2000b). A U-Pb zircon age of 70±3 Ma has been obtained by Emparan and Pineda (2000b) for the Los Elquinos Formation, in rhyodacites from the upper levels of this formation. Consequently, Late Cretaceous volcanism in the area may range from ≈90-95 Ma (assumed age for the extrusion of lower basaltic lavas of the Viñita Formation, Morata et al., 2003) up to 70-65 Ma. Based on stratigraphic and tectonic evidence (Pineda and Emparan, 1997; Emparan and Pineda, 2000b) as well as geochemical studies of volcanism (Morata and Aguirre, 2003; Morata et al., 2003), an extensional regime has been proposed during the Early Cretaceous. The geochemistry and primary isotopic signature of the Late Cretaceous basic lavas (Morata et al. 2003), suggest more intense extensional conditions during this time compared to the Early Cretaceous. The extensional volcanism cycle ended with regional caldera collapse at ca. 85 Ma (Pineda and Emparan, 1997),
© Springer Nature Switzerland AG 2021 S. Carrizo (ed.), Reverse Engineering of Ancient Metals,, 2021
Current knowledge on the beginnings of metallurgy in the Andean area is still scarce. Some new findings have been reported from tombs belonging to the Late Archaic and Middle Formative Periods, in the form of small pieces of laminated gold. In this article, we will study two gold beads scientifically excavated from contexts associated with the Middle and Late Formative Periods of the North Central coast and highlands. These gold pieces have been chemically analyzed via Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS), and the results have been compared with the available databases of pieces belonging to these periods, with the objective of unveiling the characteristics of the raw material from which they were fabricated and the changes made from one period to the next.
Nature and dimension of orogenic gold-related hydrothermal alteration at Minas Azules, NW Argentina
The extent of hydrothermal alteration associated with gold mineralization at Minas Azules in the southern Andes of northwestern Argentina has been assessed from mass-balance calculations. An alteration envelope, at least 70-to 100-m-wide, is centered along the axis of a major anticline in Ordovician turbidites. Geochemical traverses indicate that K 2 O (±Rb), CO 2 , Au, and As are consistently enriched in hydrothermally-altered psammites, whereas SiO 2 , Na 2 O, MgO, and CaO are depleted. Analysis of element dispersion patterns surrounding the Minas Azules deposit enable the development of a geochemical alteration index (A.I.) applicable to exploration for orogenic gold occurrences, with A.I. = K 2 O+CO 2 +10Icl/ K 2 O+CO 2 +10Icl+Fe 2 O 3 +TiO 2 -50As [Icl: chlorite index = MgO/MgO+Fe 2 O 3 ]. The alteration index shows a consistent increase towards the ore zone (0.53<A.I.<0.86) and permits the discrimination of hydrothermally altered turbidites from unaltered psammitic precursors (A.I. 0.49). This study confirms that orogenic gold mineralisation at Minas Azules is associated with pervasive and extensive wallrock alteration, and highlights the usefulness of hydrothermal alteration in exploration for both lode-and disseminated-style orogenic gold in Phanerozoic metamorphic terranes.
Mineralium Deposita
The 13.1-Moz high-sulfidation epithermal gold deposit of Lagunas Norte, Alto Chicama District, northern Peru, is hosted in weakly metamorphosed quartzites of the Upper Jurassic to Lower Cretaceous Chimú Formation and in overlying Miocene volcanic rocks of dacitic to rhyolitic composition. The Dafne and Josefa diatremes crosscut the quartzites and are interpreted to be sources of the pyroclastic volcanic rocks. Hydrothermal activity was centered on the diatremes and four hydrothermal stages have been defined, three of which introduced Au ± Ag mineralization. The first hydrothermal stage is restricted to the quartzites of the Chimú Formation and is characterized by silice parda, a tan-colored aggregate of quartz-auriferous pyrite-rutile ± digenite infilling fractures and faults, partially replacing silty beds and forming cement of small hydraulic breccia bodies. The δ 34 S values for pyrite (1.7-2.2‰) and digenite barite, drusy quartz, and native sulfur were deposited in the volcanic rocks. The d 18 O SO 4 values of stage IV alunite vary between 11.5 and 11.7‰ and indicate that the fluid was magmatic, an interpretation also supported by the isotopic composition of barite (δ 34 S=27.1 to 33.8‰ and d 18 O SO 4 = 8.1 to 12.7‰). The Δ 34 S py-alu isotope thermometry records temperatures of 210 to 280°C with the highest values concentrated around the Josefa diatreme. The Lagunas Norte deposit was oxidized to a depth of about 80 m below the current surface making exploitation by heap leach methods viable.