Strontium and stable C and O isotopic composition of carbonates in the Ernest Henry deposit, Queensland, Australia: implications for genesis and exploration

The Ernest Henry IOCG (iron-oxide copper gold) deposit is hosted within Paleoproterozoic meta-sedimentary and meta-igneous rocks of the eastern succession of the Mt Isa inlier. The mineralization is mostly breccia-hosted, with K-feldspar altered clasts cemented by biotite-carbonate-magnetite-sulfides. The breccias grade out to crackle breccias and then veins, with the breccia/crackle breccia contact typically demarcating economic mineralization. The origin of brecciation and mineralization remains controversial, but numerous elemental enrichments suggest multiple fluids with a mixed origin including magmatic and/or saline metamorphic fluids. Foremost among the proposed mechanism for IOCG formation at Ernest Henry is that CO2 release directly from enriched mantle, or indirectly from mafic magmas, played an important role in breccia formation and in scavenging ore components from local wallrocks, particularly mafic rocks. This hypothesis is mainly based on the regional interpretation of stable C and O isotopes from carbonates within the eastern succession of the Mt Isa inlier, including limited samples from Ernest Henry

Intermediate sulfidation type base metal mineralization at Aliabad-Khanchy, Tarom-Hashtjin metallogenic belt, NW Iran

The Aliabad-Khanchy epithermal base metal deposit is located in the Tarom-Hashtjin metallogenic belt (THMB) of northwest Iran. The mineralization occurs as Cu-bearing brecciated quartz veins hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation. Ore formation can be divided into five stages, with most ore minerals, such as pyrite and chalcopyrite being formed in the early stages. The main wall-rock alteration is silicification, and chlorite, argillic and propylitic alteration. Microthermometric measurements of fluid inclusion assemblages show that the ore-forming fluids have eutectic temperatures between −30° and −52°C, trapping temperatures of 150° to 290°C, and salinities of 6.6 to 12.4 wt.% NaCl equiv. These data demonstrate that the ore-forming fluids were medium- to high-temperature, medium- to low-salinity, and low-density H2O–NaCl–CaCl2 fluids. Calculated δ18O values indicate that ore-forming hydrothermal fluids had δ18Owater ranging from +3.6 to +0.8‰, confirming that the ore–fluid system evolved from dominantly magmatic to dominantly meteoric. The calculated 34SH2S values range from –8.1 to –5.0‰, consistent with derivation of the sulfur from either magma or possibly from local volcanic wall-rock. Combined, the fluid inclusion and stable isotope data indicate that the Aliabad-Khanchy deposit formed from magmatic-hydrothermal fluids. After rising to a depth of between 790 and 500 m, the fluid boiled and subsequent hydraulic fracturing may have led to inflow and/or mixing of early magmatic fluids with circulating groundwater causing deposition of base metals due to dilution and/or cooling. The Aliabad-Khanchy deposit is interpreted as an intermediate-sulfidation style of epithermal mineralization. Our data suggest that the mineralization at Aliabad-Khanchy and other epithermal deposits of the THMB formed by hydrothermal activity related to shallow late Eocene magmatism. The altered Eocene volcanic and volcaniclastic rocks, especially at the intersection of subvolcanic stocks with faults were the most favorable sites for epithermal ore bodies in the THMB

The Watershed tungsten deposit, NE Queensland, Australia: an example of a Permian metamorphic tungsten upgrade after a Carboniferous magmatic-hydrothermal mineralisation event

Tungsten is considered a strategic metal by various countries, including Australia. Between 1998 and 2016 Australia has been steadily increasing its tungsten production, but it is still far smaller than those of the main producers (e.g., China, Russia). Watershed with its current resources of 49.2 Mt averaging 0.14% WO3 is considered one of the biggest undeveloped tungsten deposits outside of China, and if developed would boost Australia’s tungsten production. We will be presenting the geological, geochemical and structural characteristics of the Watershed deposit, as well as the timing, mineral paragenesis and fluid characteristics of the mineralizing system; with the main goal of improving our understanding of the Watershed tungsten deposit and how to explore for similar deposits in northeast Queensland

Mineralogical distribution of germanium, gallium and indium at the Mt Carlton high-sulfidation epithermal deposit, NE Australia, and comparison with similar deposits worldwide

Germanium, gallium and indium are in high demand due to their growing usage in high-tech and green-tech applications. However, the mineralogy and the mechanisms of concentration of these critical elements in different types of hydrothermal ore deposits remain poorly constrained. We investigated the mineralogical distribution of Ge, Ga and In at the Mt Carlton high-sulfidation epithermal deposit in NE Australia, using electron probe microanalysis and laser ablation inductively-coupled plasma mass spectrometry. Parageneses from which selected minerals were analyzed include: Stage 1 acid sulfate alteration (alunite), Stage 2A high-sulfidation enargite mineralization (enargite, argyrodite, sphalerite, pyrite, barite), Stage 2B intermediate-sulfidation sphalerite mineralization (sphalerite, pyrite, galena) and Stage 3 hydrothermal void fill (dickite). Moderate to locally high concentrations of Ga were measured in Stage 1 alunite (up to 339 ppm) and in Stage 3 dickite (up to 150 ppm). The Stage 2A ores show enrichment in Ge, which is primarily associated with argyrodite (up to 6.95 wt % Ge) and Ge-bearing enargite (up to 2189 ppm Ge). Co-existing sphalerite has comparatively low Ge content (up to 143 ppm), while Ga (up to 1181 ppm) and In (up to 571 ppm) are higher. Sphalerite in Stage 2B contains up to 611 ppm Ge, 2829 ppm Ga and 2169 ppm In, and locally exhibits fine colloform bands of an uncharacterized Zn-In mineral with compositions close to CuZn2(In,Ga)S4. Barite, pyrite and galena which occur in association with Stage 2 mineralization were found to play negligible roles as carriers of Ge, Ga and In at Mt Carlton. Analyzed reference samples of enargite from seven similar deposits worldwide have average Ge concentrations ranging from 12 to 717 ppm (maximum 2679 ppm). The deposits from which samples showed high enrichment in critical elements in this study are all hosted in stratigraphic sequences that locally contain carbonaceous sedimentary rocks. In addition to magmatic-hydrothermal processes, such rocks could potentially be important for the concentration of critical elements in high-sulfidation epithermal deposits

Geology, paragenesis, and alteration patterns of the E1 group of iron oxide-Cu-Au deposits, Cloncurry district, northwest Queensland, Australia

The Proterozoic E1 Group of iron oxide-Cu-Au deposits, composed of E1 North, East, and South, is located 8 km east of the world-class Ernest Henry IOCG deposit in the Cloncurry district of northwest Queensland, and contains estimated resources of 48 Mt averaging 0.72% Cu and 0.21 g/t Au. The E1 Group has been recently discovered below 20-50 m of Mesozoic sedimentary rocks near the world-class Ernest Henry IOCG, but its relationship to that deposit is not clear. Modelling of drill data indicates that the orebody is stratigraphically controlled within a series of folded, discontinuous metatuff, metasiltstone, marble and metapsammite lenses intercalated with metabasalt and glomerophyric metaandesite. The metaandesite is likely equivalent to the intermediate volcanic rocks hosting the Ernest Henry deposit. The E1 North orebody is controlled by a NW-plunging antiform, with mineralization occurring in a single major, discontinuous metatuff lens on the east limb, and in two discontinuous metatuff lenses on the west limb. The west limb of the antiform is truncated by Corella Breccia, and the east limb continues to the southeast to form the west limb of the E1 South synform. The E1 South orebody is comprised of three discontinuous lenses within this synform, with the upper lenses hosted in metasiltstone and the lowermost lens hosted in metatuff continuing from the E1 North antiform east limb. The uppermost ore lens of E1 South grades into barren carbonaceous metapelite, and the entire E1 South system is truncated to the southeast by the Mount Margaret Fault Zone. E1 East ores are hosted in two steeply east-dipping lenses of metasilts intercalated with metabasalt and surrounded by Corella Breccia. E1 Group mineralization is characterized dominantly by fine (0.05 mm) to coarse (3 mm)-grained layer-controlled magnetite-chalcopyrite-pyrite±Fe-Mn-carbonate±barite±fluorite±biotite±albite±chlorite±apatite±arsenopyrite±pyrrhotite±monazite (tr.) ±coffinite (tr.) ±uraninite(tr.) replacement of layered metatuff and metasilt, and matrix-controlled replacement of volcaniclastic metatuff, associated with Fe-Mn-carbonate-quartz-barite-fluoritealbite-chalcopyrite-magnetite-biotite-chlorite-apatite veining. Very high-grade ores (>2% Cu) typically exhibit a massive texture which completely overprints earlier layering. This replacementdominated mineralization style is substantially different from that of the hydrothermal brecciahosted Ernest Henry orebody. The E1 paragenetic sequence is comprised of four major stages: 1) Sodic-calcic: albite-quartzhematite±actinolite±magnetite; 2) Potassic(-Fe): K-feldspar-biotite-magnetite; 3) Ore stage A: magnetite-Fe-carbonate-chalcopyrite-pyrite-quartz-barite-fluorite-biotite (±Ba-Cl)-chloriteapatite-muscovite (±Ba)-monazite; and 4) Ore stage B: Mn-(Fe)-carbonate-barite-fluorite-chalcopyrite-pyrite-quartz-sericite-arsenopyrite-pyrrhotite. Stage 1 and 2 alterations are heavily overprinted by mineralization, and are most visible immediately outside the orebody and within and proximal to the Corella Breccia. Stages 3-4 carbonate veins, accompanied by chlorite and sericite alteration, are widespread throughout the mine lease, but are most prevalent outside the orebody in the more brittle metabasalts, metaandesites and Corella Breccia. In the west limb of the E1 North antiform the carbonate veins contain abundant apatite, magnetite, and pyrite, forming a magnetic and Fe-P-rich geochemical anomaly extending 150-200m southwest from the orebody. The E1 Group and Ernest Henry share a similar paragenetic sequence of early sodic (-Ca), intermediate potassic (-Fe), and late mineralization alteration, suggesting a similar genetic origin. The reason(s) for differing mineralization styles between the two systems, despite being hosted in similar rock types, is under investigation

Geology, paragenesis, and alteration patterns of the E1 group of iron oxide-Cu-Au deposits, Cloncurry district, northwest Queensland, Australia

The Proterozoic E1 Group of iron oxide-Cu-Au deposits, composed of E1 North, East, and South, is located 8 km east of the world-class Ernest Henry IOCG deposit in the Cloncurry district of northwest Queensland, and contains estimated resources of 48 Mt averaging 0.72% Cu and 0.21 g/t Au. The E1 Group has been recently discovered below 20-50 m of Mesozoic sedimentary rocks near the world-class Ernest Henry IOCG, but its relationship to that deposit is not clear. Modelling of drill data indicates that the orebody is stratigraphically controlled within a series of folded, discontinuous metatuff, metasiltstone, marble and metapsammite lenses intercalated with metabasalt and glomerophyric metaandesite. The metaandesite is likely equivalent to the intermediate volcanic rocks hosting the Ernest Henry deposit. The E1 North orebody is controlled by a NW-plunging antiform, with mineralization occurring in a single major, discontinuous metatuff lens on the east limb, and in two discontinuous metatuff lenses on the west limb. The west limb of the antiform is truncated by Corella Breccia, and the east limb continues to the southeast to form the west limb of the E1 South synform. The E1 South orebody is comprised of three discontinuous lenses within this synform, with the upper lenses hosted in metasiltstone and the lowermost lens hosted in metatuff continuing from the E1 North antiform east limb. The uppermost ore lens of E1 South grades into barren carbonaceous metapelite, and the entire E1 South system is truncated to the southeast by the Mount Margaret Fault Zone. E1 East ores are hosted in two steeply east-dipping lenses of metasilts intercalated with metabasalt and surrounded by Corella Breccia. E1 Group mineralization is characterized dominantly by fine (0.05 mm) to coarse (3 mm)-grained layer-controlled magnetite-chalcopyrite-pyrite±Fe-Mn-carbonate±barite±fluorite±biotite±albite±chlorite±apatite±arsenopyrite±pyrrhotite±monazite (tr.) ±coffinite (tr.) ±uraninite(tr.) replacement of layered metatuff and metasilt, and matrix-controlled replacement of volcaniclastic metatuff, associated with Fe-Mn-carbonate-quartz-barite-fluoritealbite-chalcopyrite-magnetite-biotite-chlorite-apatite veining. Very high-grade ores (>2% Cu) typically exhibit a massive texture which completely overprints earlier layering. This replacementdominated mineralization style is substantially different from that of the hydrothermal brecciahosted Ernest Henry orebody. The E1 paragenetic sequence is comprised of four major stages: 1) Sodic-calcic: albite-quartzhematite±actinolite±magnetite; 2) Potassic(-Fe): K-feldspar-biotite-magnetite; 3) Ore stage A: magnetite-Fe-carbonate-chalcopyrite-pyrite-quartz-barite-fluorite-biotite (±Ba-Cl)-chloriteapatite-muscovite (±Ba)-monazite; and 4) Ore stage B: Mn-(Fe)-carbonate-barite-fluorite-chalcopyrite-pyrite-quartz-sericite-arsenopyrite-pyrrhotite. Stage 1 and 2 alterations are heavily overprinted by mineralization, and are most visible immediately outside the orebody and within and proximal to the Corella Breccia. Stages 3-4 carbonate veins, accompanied by chlorite and sericite alteration, are widespread throughout the mine lease, but are most prevalent outside the orebody in the more brittle metabasalts, metaandesites and Corella Breccia. In the west limb of the E1 North antiform the carbonate veins contain abundant apatite, magnetite, and pyrite, forming a magnetic and Fe-P-rich geochemical anomaly extending 150-200m southwest from the orebody. The E1 Group and Ernest Henry share a similar paragenetic sequence of early sodic (-Ca), intermediate potassic (-Fe), and late mineralization alteration, suggesting a similar genetic origin. The reason(s) for differing mineralization styles between the two systems, despite being hosted in similar rock types, is under investigation

The evolution and potential sources of mineralizing fluids of the E1 group of IOCG deposits, Cloncurry District, Northwest Queensland, Australia: implications from fluid inclusion and SHRIMP S isotope analyses

The E1 Group of Proterozoic iron oxide-Cu-Au deposits—E1 North, East, and South—is located 6 km east of the Ernest Henry IOCG deposit, in the far northeast of the polymetallic Cloncurry district of northwest Queensland, and hosts a total resource of 48 Mt of 0.72% Cu and 0.21 g/t Au. The mineralizing fluids of the E1 Group have not been studied in great detail and offer additional insight into the complex evolution of Cloncurry district iron oxide-associated Cu-Au deposits. We present a fluid evolution of the E1 Group hydrothermal system based on fluid inclusion microthermometrics of pre-ore, syn-early ore, and syn-late ore mineral assemblages, and ore formation temperatures calculated from in situ SHRIMP-measured sulfur isotopes in cogenetic late ore barite and chalcopyrite. The E1 Group is hosted in variably porphyritic intermediate-mafic metavolcanic rocks, marbles, metasiltstones, and carbonaceous pelites of the ~1740 Ma Corella Formation and Mount Fort Constantine Volcanics, and mineralization is characterized by layer- and matrix-controlled magnetite-carbonate-chalcopyrite ± barite ± fluorite replacement and veining of strongly sheared metasediments and metavolcanic breccias. The paragenetic sequence is characterized by four major stages: (1) early regional Na-Ca, composed mainly of albite and actinolite, (2) pre-ore K-Fe in magnetite, biotite K-feldspar, and minor quartz, (3) early Mg-Fe-carbonate-quartz-magnetite-associated mineralization, and (4) late Fe-Mn carbonate-barite-fluorite-associated mineralization. Stage 2 quartz, associated with the main phase of magnetite input, contains heterogeneously trapped, liquid-vapor ± halite, primary fluid inclusions which melt at –14°C. Stage 3 quartz, hosted in carbonate-quartz-chalcopyrite veins, is characterized by heterogeneously trapped primary, halite-saturated, hypersaline liquid-multisolid-vapor inclusions. Both stages 3 and 4 fluid inclusions homogenize above 450°C. Barite and calcite from stage 4 contain metastable liquid ± vapor inclusions with initial melting between –50° and –40°C, and final melting of ice ranging from –23° to –13°C, indicating the presence of NaCl-CaCl2–rich brine. Homogenization into the liquid phase in most inclusions occurs at temperatures >150°C, though some homogenize at ~95°C. Stage 4 chalcopyrite from E1 North, the largest of the three orebodies, shows δ34SCDT values in a narrow range between –2.2‰ and +1.9‰, while chalcopyrite δ34SCDT from E1 South are characterized by higher values ranging from 6.8‰ to 14.1‰. Sulfur in barite coeval with the chalcopyrite exhibits similar trends, with E1 North δ34SCDT of barite ranging from 16.4‰ to 21.2‰ CDT, and E1 South varying between 18.2‰ and 27.7‰. The formation temperature of stage 4 barite-chalcopyrite, calculated from sulfur isotope pairs, is constrained to 300° to 420°C in both orebodies. The transition in fluid inclusion composition from stage 3 (halite rich) to stage 4 (NaCl-CaCl2 rich), along with the decrease in minimum formation temperature (>450°C to as low as 320°C), is interpreted to represent the dilution of an early, relatively hot, sulfate-rich, and hypersaline fluid with a separate Ca-Ba–rich fluid, which was synchronous with cooling. This early fluid was likely magmatic, based on the low δ34SCDT values of E1 North chalcopyrite. Higher δ34SCDT values at E1 South may be explained by fractionation from the E1 North hydrothermal center, though the influence of primary sulfide-bearing graphitic pelites found at E1 South cannot be excluded

Fluid inclusion, zircon U-Pb geochronology, and O-S isotopic constraints on the origin and evolution of ore-forming fluids of the tashvir and varmazyar epithermal base metal deposits, NW Iran

Tashvir and Varmazyar deposits are part of the epithermal ore system in the Tarom–Hashtjin Metallogenic Belt (THMB), NW Iran. In both deposits, epithermal veins are hosted by Eocene volcanic-volcaniclastic rocks of the Karaj Formation and are spatially associated with late Eocene granitoid intrusions. The ore assemblages consist of pyrite, chalcopyrite, chalcocite, galena, and sphalerite (Fe-poor), with lesser amounts of bornite and minor psilomelane and pyrolusite. Fluid inclusion measurements from the Tashvir and Varmazyar revealed 182–287 and 194–285°C formation temperatures and 2.7–7.9 and 2.6–6.4 wt.% NaCl equivalent salinities, respectively. The oxygen isotope data suggested that the mineralizing fluids originated dominantly from a magmatic fluid that mixed with meteoric waters. The sulfur isotope data indicated that the metal and sulfur sources were largely a mixture of magma and surrounding sedimentary rocks. LA-ICP–MS zircon U–Pb dating of the granitoid intrusion at Tashvir and Varmazyar, yielded a weighted mean age of 38.34–38.31 and 40.85 Ma, respectively, indicating that epithermal mineralization developed between 40.85 and 38.31 Ma. Our data indicated that fluid mixing along with some fluid boiling were the main drives for hydrothermal alteration and mineralization at Tashvir and Varmazyar. All these characteristics suggested an intermediate-sulfidation epithermal style of mineralization. The THMB is proposed to be prospective for precious and base metal epithermal mineralization. Considering the extensional tectonic setting, and lack of advanced argillic lithocaps and hypersaline fluid inclusions, the THMB possibly has less potential for economically important porphyry mineralization

The Paleozoic Mount Carlton deposit, Bowen Basin, Northeast Australia: shallow high-sulfidation epithermal Au-Ag-Cu mineralization formed during rifting

Mount Carlton is a Paleozoic high-sulfidation epithermal deposit located in the northern segment of the Bowen Basin, northeast Queensland, Australia. The deposit is hosted in Early Permian volcanic and sedimentary rocks, and an open-pit mining operation includes the Au-rich V2 pit in the northeast and the Ag-rich A39 pit in the southwest. Mineralization at Mt. Carlton occurred during active rifting, partly contemporaneously with the deposition of volcanic sediments in localized half-graben and graben basins. Steep normal faults and fracture networks related to the rifting acted as fluid conduits and localized cores of silicic alteration. The silicic cores transition outward to zones of quartz-alunite alteration, which are, in turn, enveloped by a zone of quartz-dickite-kaolinite alteration. Epithermal mineralization at Mt. Carlton developed in three stages: Cu-Au-Ag mineralization dominated by enargite was overprinted by Zn-Pb-Au-Ag mineralization dominated by sphalerite, which, in turn, was overprinted by Cu-Au-Ag mineralization dominated by tennantite. Proximal Au-Cu mineralization in the V2 pit occurs in networks of steep faults associated with veins and hydrothermal breccias within a massive rhyodacite porphyry. Three distinct ore zones (Eastern, Western, and Link) are aligned, en echelon, along a broadly E trending corridor. The Western ore zone continues along ~600-m strike length to the southwest into the A39 pit, and it shows a metal zonation, from proximal to distal, of Au-Cu → Cu-Zn-Pb-Ag → Ag-Pb-(Cu) → Ag. Distal Ag mineralization in the A39 pit is concentrated in a volcanolacustrine sedimentary sequence that overlies the rhyodacite porphyry. It occurs in a stratabound position oriented parallel to primary sedimentary layering and locally exhibits synsedimentary ore textures. Such textures are interpreted to have formed as mineralizing fluids discharged into what most likely were lakes developed within localized rift basins, at the same time that the volcanolacustrine sediments were deposited. At depth, equivalent ore textures were produced within open spaces in the structural roots of the rift basins. 40Ar/39Ar dating of hydrothermal alunite yielded an age range of 284 ± 7 to 277 ± 7 Ma, which links the formation of the Mt. Carlton deposit to the Early Permian back-arc rifting stage in the Bowen Basin. Prolonged extension provided rapid burial of the deposit beneath a postmineralization, volcanosedimentary cover, which was essential for the exceptional preservation of Mt. Carlton. The same extension caused displacement of the rock pile along a series of shallowly dipping detachment faults and segmentation and rotation of the ore zones across steeply dipping normal faults. This deformation would have displaced any underlying porphyry mineralization relative to the current location of Mt. Carlton

High-Grade Copper and Gold Deposited During Postpotassic Chlorite-White Mica-Albite Stage in the Far Southeast Porphyry Deposit, Philippines

Ninety-eight underground diamond holes (~102 km) drilled by Far Southeast Gold Resources Inc. at the Far Southeast porphyry Cu-Au deposit, Philippines, from 2011 to mid-2013, provide a three-dimensional exposure of the deposit between 700- and –750-m elevation, with surface at ~1,400-m elevation. Far Southeast contains an inferred resource of 891.7 million tonnes (Mt) averaging 0.7 g/t Au and 0.5 wt % Cu, equivalent to 19.8 Moz Au and 4.5 Mt Cu. This contribution reports the spatial and temporal distribution of alteration and mineralization at Far Southeast, notably a white-mica–chlorite-albite assemblage that formed after early secondary biotite and before late quartz–white-mica–pyrite alteration and that is associated with the highest copper and gold grades. Alteration assemblages were determined by drill core logging, short-wavelength infrared (SWIR) spectral analysis, petrographic examination, and a quantitative evaluation of materials by scanning electron microscopy (QEMSCAN) study. Alteration is limited around sparse veins or pervasive where vein density is high and the alteration halos coalesce. The alteration and mineralization zones with increasing depth are as follows: (1) the lithocap of quartz-alunite–dominated advanced argillic-silicic alteration that hosts part of the Lepanto high-sulfidation Cu-Au epithermal deposit (mostly above ~700-m elevation), (2) an aluminosilicate-dominated zone with coexisting pyrophyllite-diaspore ± kandite ± alunite and white mica (~700- to ~100-m elevation), (3) porphyry-style assemblages characterized by stockwork veins (below ~500-m elevation), (4) the 1 wt % Cu equivalent ore shell (~400- to –300-m elevation), and (5) an underlying subeconomic zone (about –300- to –750-m elevation, the base of drilling). The ore shells have a typical bell shape centered on a dioritic intrusive complex. The paragenetic sequence of the porphyry deposit includes stage 1 granular gray to white quartz-rich (± anhydrite ± magnetite ± biotite) veins with biotite-magnetite alteration. These were cut by stage 2 lavender-colored euhedral quartz-rich (± anhydrite ± sulfides) veins, with halos of greenish white-mica–chlorite-albite alteration. The white mica is largely illite, with an average 2,203-nm Al-OH wavelength position. The albite may reflect the mafic nature of the diorite magmatism. The quartz veins of this stage are associated with the bulk of copper deposited as chalcopyrite and bornite, as well as gold. Thin Cu sulfide (chalcopyrite, minor bornite) veins with minor quartz and/or anhydrite (paint veins), with or without a white-mica halo, also occur. These veins were followed by stage 3 anhydrite-rich pyrite-quartz veins with white-mica (avg 2,197 nm, illite)–pyrite alteration halos. Combined with previous studies, we conclude that this porphyry system, including the Far Southeast porphyry and Lepanto high-sulfidation Cu-Au deposits, evolved over a period of 0.1–0.2 m.y. Three diorite porphyry stocks were emplaced, and by ~1.4 Ma biotite-magnetite–style alteration formed with quartz-anhydrite veins and deposition of ≤0.5% Cu and ≤0.5 g/t Au (stage 1); coupled with this alteration style, a barren lithocap of residual quartz with quartz-alunite halo plus kandite ± pyrophyllite and/or diaspore formed at shallower depth (>700-m elevation). Subsequently, lavender quartz and anhydrite veins with bornite and chalcopyrite (high-grade stage, avg ~1 wt % Cu and ~1 g/t Au) and white-mica–chlorite-albite halos formed below ~400-m elevation (stage 2). They were accompanied by local pyrite replacement, the formation of hydrothermal breccias and Cu sulfide (paint) veins. Stage 2 was followed at ~1.3 Ma by the formation of igneous breccias largely along the margins of the high-grade zones and stage 3 pyrite-quartz-anhydrite ± chalcopyrite veins with white-mica (mostly illitic) halos. At shallower depths in the transition to the base of the lithocap, cooling led to the formation of aluminosilicate minerals (mainly pyrophyllite ± diaspore ± dickite) with anhydrite plus high-sulfidation-state sulfides and pyrite veinlets. Consistent with previous studies, it is likely that the lithocap-hosted enargite-Au mineralization formed during this later period