Carboniferous Orogenic Gold Deposits at Pataz, Eastern AndeanCordillera, Peru: Geological and Structural Framework, Paragenesis, Alteration,and 40Ar/39Ar Geochronology (original) (raw)
Related papers
Earth and Planetary Science Letters, 2006
Major and trace element concentrations and Nd isotope compositions of Ordovician volcano-intrusive rocks in the Puna region of northwestern Argentina suggest formation in a pericratonic setting above thickened and evolved continental crust. Input from juvenile sources was limited and there is no evidence for oceanic crust or the presence of a terrane-bounding suture in the study region. Geochronological constraints from 40 Ar/ 39 Ar (sericite-rich whole-rock) and Re-Os (arsenopyrite-pyrite) dating indicate initial deposition of gold in the turbidite-dominated Sierra de Rinconada during orogenic events in the Late Ordovician. This period corresponds to an epoch of major continental growth that includes development of abundant gold deposits along the long-lived and extensive accretionary margins of Gondwana. The ca. 440 Ma mineralisation ages represent the oldest recorded timing of gold emplacement in the central Andes. These ages also coincide with ca. 440 Ma ages obtained for the timing of mineralisation in each of the four largest orogenic gold deposits in the western Lachlan Orogen of eastern Australia. In contrast to analogous terranes elsewhere in the Central Andes (e.g., Peru and Bolivia), however, the Palaeozoic succession in northwest Argentina hosts relatively minor gold mineralisation. Possible explanations for the lack of a more substantial gold endowment include the (i) specific tectonic evolution of this region, (ii) absence of hydrated oceanic substrate in the northern Puna, (iii) lack of first-order, trans-crustal conduits, (iv) restriction of possible asthenospheric upwelling to a short period in the Early Ordovician, and (v) relatively limited extent of crustal shortening and thickening during Ordovician and subsequent orogenic events, when compared to analogous Palaeozoic metamorphic terrains elsewhere that are characterised by substantial orogenic gold endowment.
Ancient structural inheritance explains gold deposit clustering in northern Perú
Geology
The punctuated distribution of major gold deposits along orogenic belts is poorly understood. In northern Perú, gold deposits cluster along trends that transect the subparallel Phanerozoic belts that accreted onto the western margin of the Archean–Proterozoic Amazonian craton. This suggests the influence of as yet unrecognized pre-Andean basement structures in controlling the localization of Phanerozoic deposits. We report the newly discovered Tomac ophiolite, which represents a missing link in tracing a cryptic basement collisional suture striking obliquely to the Peruvian Andes. The Tomac ophiolite signals the opening of a former Neoproterozoic ocean basin between the Amazonian craton and a continental ribbon of dispersed microterranes. Re-accretion of the continental ribbon resulted in the formation of a collisional belt between ca. 465 and 440 Ma. Rifting and re-accretion occurred parallel to the strike of the ca. 1400–1000 Ma Grenvillian-Sunsás orogen, indicating that structura...
Mineral Deposit Research: Meeting the Global Challenge, 2005
Major and trace element concentrations, and Nd isotope compositions of Ordovician volcano-intrusive rocks in the Puna of northwestern Argentina point to their formation in a pericratonic setting above thickened and evolved continental crust. Input from juvenile sources was limited and there is no evidence for oceanic crust or the presence of a terrane-bounding suture in the region. In contrast to analogous terrains elsewhere in the Central Andes (e.g., in Peru and Bolivia), relatively minor orogenic gold mineralisation is known to occur in the Palaeozoic succession in northwestern Argentina. Possible explanations for the lack of more substantial orogenic gold endowment include the absence of hydrated oceanic substrate in the Puna, lack of 1 st -order conduits and the limited extent of crustal shortening and thickening during Ordovician orogenic events.
Multiple Gold Mineralizing Styles in the Northern Pataz District, Peru
Multiple Gold Mineralizing Styles in the Northern Pataz District, Peru, 2016
Gold production from the northern Pataz district in the eastern Andean Cordillera of Peru has been sourced mainly from mesothermal quartz-carbonate-sulfide veins hosted by the Mississippian Pataz batholith. Gold is also found in basement-hosted veins underlying the batholith, in the Vijus-Santa Filomena area of the district. Both are located within a central horst; similar vein mineralogy and proximal phengitic white mica alteration are common to both. However, comb-textured quartz, the chemical compositions of bulk ore and sulfide minerals , and the presence of barite and siderite veins suggest that the basement-hosted veins formed at a shallower crustal level. Similar expressions of hydrothermal alteration associated with anomalous gold, As, Sb, and Tl are also present in the adjacent Lavasen graben, where alteration is intimately associated with volcanic processes that deposited the Mississippian Lavasen Volcanics. K-Ar and 40 Ar-39 Ar ages for hydrothermal illite from all three locations range between Mississippian and Late Triassic but are consistent with a single Mississippian hydrothermal event, if the data record a minimum age for original illite formation. The geologic setting, miner-alization styles, and chemical data suggest a range of crustal depths, ranging from mesothermal batholith-hosted veins through shallow to intermediate depths for the Vijus-Santa Filomena area to a near-surface epithermal setting for the Misquichilca area. Telescoping of this 10-to 13-km crustal range into a 3-km topographic section of the Andes is attributed to syn-and postmineralization uplift and erosion. Sulfide-rich high-grade ore shoots and moderately saline fluid inclusions in the batholith-hosted veins are inconsistent with the original orogenic gold model and suggest a magmatic source component for the ore fluid, consistent with stable isotope (O, H, C, and S) compositions of quartz, illite, carbonates, and sulfides. The isotopic data suggest a mixed magmatic-meteoric ore fluid in the basement-hosted deposits of the Vijus-Santa Filomena area and the volcanic-hosted Misquichilca area. Both the Pataz batholith and the Esperanza Subvolcanic Complex are of the same Mississippian age as the hydrothermal alteration and mineralization. The Esperanza Subvolcanic Complex, comagmatic with the Lavasen Volcanics, contains cognate mineral clots from which a subjacent magma chamber can be inferred. It exhibits potassic, calc-silicate, and argillic alteration, and evidence for the evolution of an Fe-rich volatile phase. The Lavasen-Esperanza magma suite is ferroan and weakly alkaline, with A-type affinities. These features provide a conceptual genetic link with hydrothermal alteration associated with gold mineralization, including Fe (±As) sulfides, phengitic white mica, celadonite, Fe-rich carbonates, and less common Fe oxides. An oxidized intrusion-related model is proposed for gold and hydrothermal alteration in the northern Pataz district.
Economic Geology, 2008
A compilation of economically viable gold concentrations containing ≥10 Moz in the North and South American Cordillera reveals the existence of 22 discrete belts in addition to five major isolated deposits, most formed over the last 150 m.y. The gold concentrations are attributed to eight widely recognized deposit types, of which porphyry, sediment-hosted, and high-sulfidation epithermal are economically the most important. Individual gold belts are typically several tens to hundreds of kilometers long, dominated by single deposit types, and metallogenically active for relatively brief periods (<5-20 m.y.). Many of the gold belts and major isolated deposits were generated under extensional or transtensional tectonic conditions in either arc or back-arc settings. Nevertheless, the two main high-sulfidation epithermal gold belts were generated in thickening or already-thickened crust during low-angle subduction. Eight other gold belts or districts also accompanied compression or transpression, with two of them, the main orogenic gold belts, occupying fore-arc sites. There is a strong suggestion that the preeminent Cordilleran gold concentrations formed either during or immediately following prolonged contraction. The major gold deposits and belts occur along the craton edge as well as in adjoining accreted terranes, but almost all are of postaccretionary timing. Many of the gold belts and isolated deposits were localized by crustal-scale faults or lineaments, which may be either parallel or transverse to the Cordilleran margin. The gold concentrations accumulated during active subduction, commonly in close spatial and temporal association with intermediate to felsic, medium-to high-K calc-alkaline igneous rocks. By contrast, the lowsulfidation epithermal gold deposits accompany bimodal volcanic pulses of calc-alkaline, tholeiitic, or alkaline affinity. However, a gold-alkaline rock association is uncommon. A genetic link between gold mineralization and coeval magmatism is widely accepted for most of the deposit types, the exceptions being the sedimenthosted and orogenic gold deposits. Notwithstanding the small cumulative extent of the gold concentrations relative to the entire Cordilleran margin, there is a marked tendency for two or more belts or isolated deposits of different ages and genetic types to occur in close proximity within relatively restricted arc (including fore-and back-arc) segments. In the case of the western United States, for example, six belts and four isolated major deposits make up a particularly prominent cluster. If fortuity is discounted, this clustering or pairing of gold concentrations must imply a predisposition of certain arc segments to gold mineralization. An analogous situation is evident for other metals, particularly copper and tin. The reason for the recurrent generation of major deposits and belts dominated by one or more metals remains uncertain, although heterogeneously distributed metal preconcentrations, favorable redox conditions, or other parameters somewhere above the subducted slab, between the mantle wedge and upper crust, are widely contemplated possibilities. Elucidation of the reason(s) for this metallogenic inheritance at the scale of limited arc segments poses an important and challenging series of research questions as well as being critical to the planning of potentially successful greenfield exploration programs.
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.