Porphyry Copper-molybdenum Deposit Research Articles

Origin and Geological Implications of Monzogranites and Rhyolitic Porphyries in the Wunugetu Porphyry Copper–Molybdenum Deposit, Northeast China: Evidence from Zircon U-Pb-Hf Isotopes and Whole-Rock Geochemistry

The Wunugetu deposit, a large-scale porphyry copper–molybdenum deposit, is located in the southern Erguna block. Its ore bodies are primarily found within monzogranites, granite porphyries, and biotite monzogranites. Additionally, the deposit contains late-stage intrusive dykes of rhyolitic porphyries. This study examined the deposit’s monzogranites and rhyolitic porphyries using lithogeochemistry, zircon U-Pb dating, and Hf isotopic analysis. The main findings include: (1) Zircon U-Pb dating showed that the monzogranites formed around 209.0 ± 1.0 Ma, whereas the rhyolitic porphyries in the northern portion formed around 170.49 ± 0.81 Ma, suggesting magmatic activity in the deposit spanned from the Late Triassic to the Middle Jurassic. (2) The monzogranites exhibited high silicon content (73.16–80.47 wt.%) and relatively low aluminum content (10.98–14.37 wt.%). They are enriched in alkalis (content: 3.42–10.10 wt.%) and deficient in magnesium and sodium, with aluminum saturation indices (A/CNK) ranging from 1.1 to 2.9. In addition, the monzogranites are enriched in large-ion lithophile elements (LILEs) such as Rb, K, and Ba and deficient in high-field-strength elements (HFSEs) like Nb, P, and Ti. (3) The monzogranites have low Zr + Nb + Ce + Y contents of (151.3–298.6 ppm) × 10−6 and 10,000 × Ga/Al ratios varying between 1.20 and 2.33, suggesting that they are characteristic of I-type granites. (4) Positive zircon εHf(t) values ranging from +0.3 to +7.6 in both rhyolitic porphyry and monzogranite samples, increasing with younger emplacement ages, imply that the deposit’s rocks originated from magmatic mixing between mantle-derived mafic magmas and remelts of the juvenile crust. Considering these results and the regional geological evolution, this study proposes that the Wunugetu deposit was formed in an active continental margin setting and was influenced by the Late Triassic–Middle Jurassic southeastward subduction of the Mongol-Okhotsk Ocean.

Occurrence State and Enrichment Mechanism of Rhenium in the Qianjiadian Uranium Deposit in the Southwestern Songliao Basin, Northeast China

Rhenium is an extremely rare critical metal element in Earth’s continental crust. Owing to its extremely high melting point and heat-stable crystalline structure, rhenium is an essential component of alloy materials used in high-performance aircraft engines. Demand for rhenium resources is therefore growing. Currently, most rhenium is produced as a byproduct of molybdenum mining in porphyry copper–molybdenum deposits. Research has therefore focused on the enrichment characteristics of rhenium in this type of deposit, with little attention paid to rhenium in other types of deposits. This study reports the occurrence state and enrichment mechanism of rhenium in the Qianjiadian sandstone-type uranium deposit in the Songliao Basin, Northeast China. Sequential extraction revealed that the average proportions of different forms of rhenium are as follows: water-soluble (57.86%) > organic-sulfide-bound (13.11%) > residual (12.26%) > Fe/Mn oxide-bound (10.67%) > carbonate-bound (6.10%). Combining mineralogical analysis techniques such as SEM-EDS, EMPA, and XRD, it has been established that rhenium does not occur as a substitute in sulfides (e.g., molybdenite) or uranium minerals in various types of deposits. Instead, it is mainly adsorbed onto clay minerals and Fe-Ti oxides, and in a small number of other minerals (pyrite, organic matter, and pitchblende). Rhenium is similar to redox-sensitive elements such as uranium and vanadium, and it is transported in a water-soluble form by oxidizing groundwater to the redox transition zone for enrichment. However, unlike uranium, which generally forms as uranium minerals, rhenium is mainly adsorbed and enriched onto clay minerals (kaolinite and interlayered illite–smectite). Most of the rhenium in sandstone-type uranium deposits occurs in an ion-adsorption state, and is easily leached and extracted during in-situ leaching mining of uranium ores. This type of deposit demonstrates excellent production potential and will become a crucial recoverable resource for future rhenium supply.

Geochemical Characteristics of Primary Halos and Prospecting Significance of the Qulong Porphyry Copper–Molybdenum Deposit in Tibet

The Qulong porphyry copper deposit in Tibet is located in the Tethis–Himalaya metallogenic domain, one of the three major porphyry metallogenic domains in the world. At present, the mining area is mainly used for surface mining. The depth revealed by the drilling project is less than 2 km. The potential for deep resources is unknown. Based on an analysis of the geochemical characteristics of the primary halos around the No. 16 prospecting line, deep extension is discussed in this paper. Studies show that the metallogenic elements are Cu and Mo; the near-ore halo elements are Co, Au, Ag, and W; the supra-ore halo elements are Pb, Zn, Mn, and As; and the sub-ore halo elements are Sn and Bi. According to Gregorian’s zoning index and the barycenter method, the primary halo zoning of the No. 16 exploration line from shallow to deep is Mn–P–Pb–Ni–Zn–V–As–Hg–Co–Au–Cu–W–Ag–Mo–Sb–Sr–Cd–Sn–Ti–Bi. This sequence has a distinct “reverse” zoning feature, indicating that there may be a blind ore body deep in the mine. The geochemical parameter evaluation index based on the element content contrast coefficient suggests that there may be a hidden ore body in the deep. The relative hydrothermal mineralization in the center position of the section may be located deep below the north side of borehole ZK1601-1 in the middle of the section. The ore body erosion parameter model shows that the bottom of the drilling engineering control is the middle tail of the ore body, and there is a certain amount of extension in the deep part. The ideal superimposed model of the primary halo reflects the ore body trend of the 16th line section. The ore body is inclined to the north as a whole; the ore fluid flows from the deep to the southern side of the north side, and the deep part of the northern side of the ore body has a downward trend.

Protracted Magmatism and Mineralized Hydrothermal Activity at the Gibraltar Porphyry Copper-Molybdenum Deposit, British Columbia

Abstract The Gibraltar Cu-Mo deposit, with a total tonnage of 3.2 million tons (Mt) Cu, is located in the Canadian Cordillera and hosted by the Late Triassic Granite Mountain batholith. The batholith formed through multiple intrusions of tonalitic rocks over a period of ~25 m.y. beginning at 229.2 ± 4.4 Ma in the Quesnel island arc before the accretion of the arc to the North American continent. Late in its evolution, Cu fertile magmas intruded in the center of the batholith, during at least three events from 218.9 ± 3.1 to 205.8 ± 2.1 Ma. The fertile magmas were hotter and more mafic than older barren magmas. They generated magmatic-hydrothermal activity, forming potassic alteration and white mica alteration, and produced Cu mineralization as chalcopyrite-quartz veinlets and disseminated chalcopyrite. Zircon in the Cu-bearing tonalite intrusion (218.9 ± 3.1 Ma) shows high Ce4+/Ce3+ (681 ± 286 [2σ], n =15) compared to those from older barren intrusions (129 ± 56 [2σ], n = 118). Oxidation conditions for parental magmas are calculated using the compositions of zircon and amphibole. The magmas for Cu-bearing intrusions have an average of fayalite-magnetite-quartz buffer (FMQ) +1.7 ± 0.7 (2σ, n = 73), whereas those for older barren intrusions have slightly lower fO2 (avg FMQ +1.3 ± 0.5 [2σ], n = 108), although the values are overlapping for the two. The bulk rocks of Cu-bearing tonalite intrusions in the Granite Mountain batholith have low Sr/Y ratios (<22) independent of the degrees of alteration. The low ratios are also reflected by low Sr/Y in zircon, suggesting that the low Sr/Y ratios of bulk rocks represent those of unaltered rocks. The values are low compared to those associated with many other porphyry Cu deposits globally. The data suggest that igneous rocks elsewhere with low Sr/Y in bulk rocks may have a potential to host economic Cu deposits. Ratios of Ce/Nd and Ce/Ce* (=Ce/((NdN)2SmN)) in zircon are positively correlated with the Ce4+/Ce3+ in zircon from the Granite Mountain batholith. Since the former two ratios can be obtained solely from zircon composition, these ratios from detrital zircon may be useful in evaluating the occurrences of oxidized intrusions in regional mineral exploration.

Geochemical and Petrology Properties of Zafarghand Index and Kahang Deposit of Porphyry Copper-Molybdenum

The probability of the occurrence of porphyry copper ore associated with subduction zone of the Neo-Tethys ocean and volcanic arc of Iran (Urumieh-Dokhtar) justifies the necessity of exploration and prospection of this type of ore in Iran. Zafarghand index and Kahang deposit of porphyry copper-molybdenum located in Isfahan province, center of Iran using Satellite data interpretations were discovered in the years of 2010 and 2003, respectively. Geological studies have indicated the presence of argillic and propylitic alteration halos associated with porphyry copper systems. The 250 rock samples were systematically collected at a sampling distance of 100 m and in the center of the porphyry system by a distance o f 50 m in Zafarghand. Also, 377 samples of lithogeochemicals (185 rock samples and 192 soil samples) were extracted systematically from Kahang deposit. The study of geochemical data of rock and soil samples showed similarity of these two types of mineralization with other mineralization of porphyry copper-molybdenum elsewhere in the world. Finally, the comparison of geochemical anomalies copper with rock units and alteration zones showed that atmospheric waters had washed out the copper in some of these zones and probably the supergene zone was formed in depth as porphyry copper-molybdenum deposit.

Critical Metal Particles in Copper Sulfides from the Supergiant Río Blanco Porphyry Cu–Mo Deposit, Chile

Porphyry copper–molybdenum deposits (PCDs) are the world’s most important source of copper, molybdenum and rhenium. Previous studies have reported that some PCDs can have sub-economic to economic grades of critical metals, i.e., those elements that are both essential for modern societies and subject to the risk of supply restriction (e.g., platinum group elements (PGE), rare earth elements (REE), In, Co, Te, Ge, Ga, among others). Even though some studies have reported measured concentrations of Pd and Pt in PCDs, their occurrence and mineralogical forms remain poorly constrained. Furthermore, these reconnaissance studies have focused predominantly on porphyry Cu–Au deposits, but very limited information is available for porphyry Cu–Mo systems. In this contribution, we report the occurrence of critical metal (Pd, Pt, Au, Ag, and Te) inclusions in copper sulfides from one of the largest PCDs in the world, the supergiant Río Blanco-Los Bronces deposit in central Chile. Field emission scanning electron microscope (FESEM) observations of chalcopyrite and bornite from the potassic alteration zone reveal the presence of micro- to nano-sized particles (<1–10 μm) containing noble metals, most notably Pd, Au, and Ag. The mineralogical data show that these inclusions are mostly tellurides, such as merenskyite ((Pd, Pt) (Bi, Te)2), Pd-rich hessite (Ag2Te), sylvanite ((Ag,Au)Te2) and petzite (Ag3AuTe2). The data point to Pd (and probably Pt) partitioning in copper sulfides during the high-temperature potassic alteration stage, opening new avenues of research aimed at investigating not only the mobility of PGE during mineralization and partitioning into sulfides, but also at exploring the occurrence of critical metals in porphyry Cu–Mo deposits.

Comparative study of mineral chemistry of four biotite types as geochemical indicators of mineralized and barren intrusions in the Sungun Porphyry Cu-Mo deposit, northwestern Iran

The Sungun Porphyry copper-molybdenum deposit, in the northwestern part of the post-collisional Urumieh-Dokhtar magmatic arc, developed as a consequence of hydrothermal alteration related to the emplacement of the Sungun quartz monzonite porphyry stock into Eocene volcanic rocks. Based upon petrographic characteristics, back-scattered electron images, and compositional attributes, biotite from the Sungun Porphyry copper-molybdenum deposit was grouped into least-altered magmatic biotite (LA-Mbt), least-altered equilibrated magmatic biotite (LA-Eq Mbt), equilibrated magmatic biotite (Eq-Mbt), and secondary hydrothermal biotite (S-Hbt) types. The LA-Mbt from the mineralized zone have high TiO2 (3.92–4.33 wt%) compared to LA-Eq Mbt (3.81–4.20 wt%), Eq-Mbt (2.75–3.85 wt%), and S-Hbt (0.27–3.00 wt%). The LA-Mbt of the barren dike is also characterized by high TiO2 (4.17 wt% on average). Na2O, SiO2, and MnO (wt%) of biotite are systematically different between mineralized intrusions and barren ones. The highest amounts of Na2O (0.39–0.58 wt%) and MnO (0.11–0.18 wt%) are found in the LA-Mbt of the barren dike, which contrast with LA-Mbt of the mineralized zone having 0.08–0.15 wt% Na2O and 0.03–0.14 wt% MnO. Low SiO2 values (36 wt% on average) are characteristic of LA-Mbt from the barren dike in comparison with LA-Mbt of the mineralized zone (37 wt% on average). The SO3 contents in LA-Mbt of the mineralized zone (0.03–0.12 wt%) are much higher than those for LA-Mbt of the barren dike (0.01–0.04 wt%). The fluctuations in SO3 content of S-Hbt reflect a complex history of formation of S-Hbt in two stages. One group of S-Hbt has SO3 > 0.04 wt% and are principally related to the potassic (medium–high)/phyllic (low) assemblage, forming with magnetite at high oxygen fugacity, whereas the second group has SO3 < 0.04 wt% and is related to the phyllic (high)/argillic (low) assemblage, having formed during a stage of sulfide mineralization. The calculated oxygen fugacities (ƒO2) of 10−15.4–10−13.8 for the mineralized zone of the Sungun Porphyry Cu-Mo deposit lie completely within the domain of logƒO2 > ΔFMQ+2 (where FMQ is the fayalite–magnetite–quartz oxygen buffer), typical of oxygen fugacities associated with Cu-Mo porphyry mineralization. Altered biotite types have higher Cl contents than the least altered varieties, indicating that Cl may be used as an indicator of post-magmatic hydrothermal processes. The range of F contents (0.336–0.621 wt%) for the LA-Mbt of the mineralized zone is higher than those of the LA-Mbt types of the barren dike (0.219–0.347 wt%). Fluorine in biotite may be used as an exploration vector to characterize mineralized versus subeconomic porphyry Cu-Mo systems.

Dissecting the Re-Os molybdenite geochronometer

Rhenium and osmium isotopes have been used for decades to date the formation of molybdenite (MoS2), a common mineral in ore deposits and the world’s main source of molybdenum and rhenium. Understanding the distribution of parent 187Re and radiogenic daughter 187Os isotopes in molybdenite is critical in interpreting isotopic measurements because it can compromise the accurate determination and interpretation of mineralization ages. In order to resolve the controls on the distribution of these elements, chemical and isotope mapping of MoS2 grains from representative porphyry copper-molybdenum deposits were performed using electron microprobe and nano-scale secondary ion mass spectrometry. Our results show a heterogeneous distribution of 185,187Re and 192Os isotopes in MoS2, and that both 187Re and 187Os isotopes are not decoupled as previously thought. We conclude that Re and Os are structurally bound or present as nanoparticles in or next to molybdenite grains, recording a complex formation history and hindering the use of microbeam techniques for Re-Os molybdenite dating. Our study opens new avenues to explore the effects of isotope nuggeting in geochronometers.

Direct block-support simulation of grades in multi-element deposits: application to recoverable mineral resource estimation at Sungun porphyry copper-molybdenum deposit

Direct block-support simulation of grades in multi-element deposits: application to recoverable mineral resource estimation at Sungun porphyry copper-molybdenum deposit

Geologic and geochemical insights into the formation of the Taiyangshan porphyry copper–molybdenum deposit, Western Qinling Orogenic Belt, China

Taiyangshan is a poorly studied copper–molybdenum deposit located in the Triassic Western Qinling collisional belt of northwest China. The intrusions exposed in the vicinity of the Taiyangshan deposit record episodic magmatism over 20–30millionyears. Pre-mineralization quartz diorite porphyries, which host some of the deposit, were emplaced at 226.6±6.2Ma. Syn-collisional monzonite and quartz monzonite porphyries, which also host mineralization, were emplaced at 218.0±6.1Ma and 215.0±5.8Ma, respectively. Mineralization occurred during the transition from a syn-collisional to a post-collisional setting at ca. 208Ma. A barren post-mineralization granite porphyry marked the end of post-collisional magmatism at 200.7±5.1Ma. The ore-bearing monzonite and quartz monzonite porphyries have a εHf(t) range from −2.0 to +12.5, which is much more variable than that of the slightly older quartz diorite porphyries, with TDM2 of 1.15–1.23Ga corresponding to the positive εHf(t) values and TDM1 of 0.62–0.90Ga corresponding to the negative εHf(t) values. Molybdenite in the Taiyangshan deposit with 27.70 to 38.43ppm Re suggests metal sourced from a mantle–crust mixture or from mafic and ultramafic rocks in the lower crust. The δ34S values obtained for pyrite, chalcopyrite, and molybdenite from the deposit range from +1.3‰ to +4.0‰, +0.2‰ to +1.1‰, and +5.3‰ to +5.9‰, respectively, suggesting a magmatic source for the sulfur. Calculated δ18Ofluid values for magmatic K-feldspar from porphyries (+13.3‰), hydrothermal K-feldspar from stockwork veins related to potassic alteration (+11.6‰), and hydrothermal sericite from quartz–pyrite veins (+8.6 to +10.6‰) indicate the Taiyangshan deposit formed dominantly from magmatic water. Hydrogen isotope values for hydrothermal sericite ranging from −85 to −50‰ may indicate that magma degassing progressively depleted residual liquid in deuterium during the life of the magmatic–hydrothermal system. Alternatively, δD variability may have been caused by a minor amount of mixing with meteoric waters. We propose that the ore-related magma was derived from partial melting of the ancient Mesoproterozoic to Neoproterozoic middle to lower continental crust. This crust was likely metasomatized during earlier subduction, and the crustal magmas may have been contaminated with lithospheric mantle derived magma triggered by MASH (e.g., melting, assimilation, storage, and homogenization) processes during collisional orogeny. In addition, a significant proportion of the metals and sulfur supplied from mafic magma were simultaneously incorporated into the resultant hybrid magmas.

Metallogenic events and tectonic setting of the Duobaoshan ore field in Heilongjiang Province, NE China

The Duobaoshan ore field, a major center of metal production in Northeast China, is located in the northeast of the Xing’an–Mongolia Orogenic Belt (the eastern part of the Central Asian Orogenic Belt) and within the northern Greater Xing’an Mountains. Several types of ore deposits are mined in the Duobaoshan region, including the Duobaoshan and Tongshan porphyry copper–molybdenum deposits, the Sankuanggou skarn iron–copper deposit, and the Zhengguang epithermal gold deposit. Zircon grains from the Tongshan granodiorite and porphyritic granite yield laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U–Pb weighted mean ages of 475.9±0.8Ma and 230.9±0.9Ma to 240.7±0.8Ma, respectively. The Re–Os isochron age of molybdenites from the Tongshan deposit is 473±4Ma. Because both field observations and petrographic analysis identified disseminated chalcopyrite, pyrite, and malachite in the porphyritic granite, the isotope dating indicates that the Tongshan deposit underwent at least two magmatic–mineralization events, during the Ordovician and the Triassic. Zircon grains from the metallogenic granodiorite of the Sankuanggou skarn deposit yield an age of 176.1±0.3Ma, and Re–Os dating of molybdenite gives an age of 173±6Ma, indicating a Jurassic event. Based on previous research and the new geochemical analysis presented in this study, it is inferred that the magmatism and mineralization of the Sankuanggou deposit were associated with the subduction of the Paleo-Pacific Plate. The Duobaoshan region has therefore experienced at least three major magmatic and mineralization events, during the Ordovician (470–480Ma), the Triassic (230–240Ma), and the Early Jurassic (170–180Ma).

Molybdenite as a Rhenium Carrier: First Results of a Spectroscopic Approach Using Synchrotron Radiation

The chemical and physical properties of rhenium render it a highly demanded metal for advanced applications in important industrial fields. This very scarce element occurs mainly in ores of porphyry copper-molybdenum deposits associated with the mineral molybdenite, MoS2, but it has also been found in granite pegmatites and quartz veins as well as in volcanic gases. Molybdenite is a typical polytype mineral which crystal structure is based on the stacking of [S-Mo-S] with molybdenum in prismatic coordination by sulphide anions; however, it is not yet clearly established if rhenium ions replace Mo4+ cations in a disordered way or else, if such replacement gives rise to dispersed nanodomains of a rhenium-rich phase. As a contribution to clarify this question, an X-ray absorption spectroscopy (XANES) study using synchrotron radiation was performed at the Re L3-edge of rhenium-containing molybdenite samples. Obtained results are described and discussed supporting the generally accepted structural perspective that rhenium is mainly carried by molybdenite through the isomorphous replacement of Mo, rather than by the formation of dispersed Re-specific nanophase(s).

LONGEVITY OF PORPHYRY COPPER FORMATION AT QUELLAVECO, PERU

Metal introduction at the late Paleocene to early Eocene Quellaveco porphyry copper-molybdenum deposit in southern Peru spans several phases of quartz monzonite porphyry emplacement and is bracketed by a precursor granodiorite pluton and a late-mineral porphyry body that postdates essentially all copper introduction. Together, the U-Pb ages of zircons from these intrusive rocks show that 1.08 ± 0.58 m.y. elapsed between the precursor pluton and initiation of stock emplacement; the porphyry system was active intermittently for at least 3.25 m.y. (4.07 ± 0.82 m.y.); and at least three-quarters of the copper inventory was deposited in a maximum of 3.12 m.y. (2.51 ± 0.61 m.y.). Recent U-Pb zircon dating of several other major central Andean porphyry copper deposits, in combination with other isotopic techniques, suggests that 2.5- to 4-m.y. life spans are commonplace. The longevity of porphyry copper systems implied by these studies appears to reflect the protracted time gaps between the multiple intrusions that intermittently replenished porphyry stocks. Other precise isotopic methods (Re-Os, 40 Ar/ 39 Ar) typically document shorter life spans because it is more difficult, if not impossible, to date the full sequence of events involved in porphyry copper formation.

Tourmaline in the Vetka porphyry copper-molybdenum deposit of the Chukchi Peninsula of Russia

Three generations of tourmaline have been identified in propylite in the Vetka porphyry copper-molybdenum deposit of the Chukchi Peninsula of Russia. Tourmaline-I is characterized by its Fetot/(Fetot + Mg) value, which ranges from 0.33 to 0.49. Tourmaline-II, which crystallizes at a lower temperature, overgrowing tourmaline-I or occurring as isolated crystals, is distinguished by a higher Fetot/(Fetot + Mg), which varies from 0.46 to 0.72. The Fetot/(Fetot + Mg) ratio in tourmaline-III, which overgrows tourmaline-II is lower (0.35–0.49), and is identical to that of the first tourmaline generation. This is probably caused by the beginning of sulfide deposition. Tourmalines in the deposit characterized by complex isomorphic substitutions can be attributed to the intermediate members of the dravite—“hydroxy-uvite”-“oxy-uvite” and schorl-“hydroxy-feruvite”-“oxy-feruvite” series. Tourmaline starts to crystallize at temperatures above 340°C. The fluid responsible for the tourmaline deposition was magmatic, with a significant admixture of meteoric water (δ18OH2O = −0.85 to −0.75‰). The high Fe3+/Fetot ratio (0.50) indicates high oxygen activity when the tourmaline precipitated. It has been established that the isomorphic substitution Fetot → Al is typomorphic of tourmalines from porphyry copper deposits worldwide.

The gold-silver Okhotsk-Chukotka volcanic belt

The Okhotsk-Chukotka volcanic belt (OChVB) formed over 25 Ma from the middle Albian to the Cenomanian at the boundary of the continental Verkhoyansk-Chukotka and the Koryak-Kamchatka collages of terranes as a special tectonic unit of the Earth℉s crust composed of subaerial volcanic rocks extending for 3000 km. In regard to the oceanic margin, the inner, outer, and flank zones of the OChVB have been recognized. The complex structure of terranes in the basement and the OChVB itself resulted in the formation of diverse epithermal deposits. Porphyry copper-molybdenum deposits are concentrated in the inner zone. The outer zone is characterized by gold-silver ore mineralization and a variety of tin deposits. Silver-base-metal deposits (Dukat, Lunny, Arylakh, etc.) are confined to the rift-related volcanic trough that complicates the OChVB between the Yana-Kolyma and Omolon terranes.

Geology of the post-collisional porphyry copper–molybdenum deposit at Qulong, Tibet

Porphyry deposits are usually thought to form from subduction-related calc-alkaline magmas in magmatic arc settings, although some porphyry deposits also occur in post-collisional extensional settings. The post-collisional deposits remain poorly understood. Here we describe the igneous geology, alteration mineralogy and mineralization history of Qulong, a newly-discovered porphyry Cu–Mo deposit in southern Tibet that belongs to the post-collisional class. The deposit is associated with Miocene monzogranite–granodiorite intrusions and is hosted partly by Jurassic andesitic–dacitic volcanic rocks. The deposit contains 7.1 Mt Cu and 0.5 Mt Mo metal. The ~ 19.5 Ma granodioritic–monzogranitic Rongmucuola pluton with diorite enclaves is the earliest Miocene intrusive unit. It was intruded by a regularly-shaped stock (P porphyry) and then thin dikes (X porphyry) of monzogranite at about 17.7 Ma. The main Cu–Mo mineralization is associated with the P porphyry. A barren diorite porphyry intruded the P and X porphyries around 15.7 Ma. Petrologic trends of the intrusions suggest that the Miocene intrusions have similar origins and probably formed by fractionation of a deeper magma chamber. Emplacement of Miocene porphyries, controlled by the Qulong anticline, is in direct response to the rapid uplift/erosion of the Gangdese arc batholiths in southern Tibet. Miarolitic cavities and unidirectional solidification textures, key evidence for volatile separation, have been recognized in the P and X porphyries, respectively. Early potassic alteration, characterized by quartz–K feldspar (± anhydrite), pervades the P porphyry and Rongmucuola pluton. Laterally, this alteration grades into quartz–biotite–anhydrite (± K feldspar), which affects all Miocene intrusions except the latest dioritic porphyry. Wall rocks of Rongmucuola pluton and Jurassic andesitic–dacitic volcanics within 1–1.5 km of the porphyries are dominated by pervasive potassic alteration. An outer halo of propylitic alteration (epidote–chlorite ± calcite) extends up to 2 km away from the deposit. Feldspar-destructive alteration (sericite–chlorite ± clay minerals) has overprinted most of the potassic and part of the propylitic alteration. The alteration is strongly pervasive in the interior of the porphyry bodies and occurs as vein halos away from the porphyry bodies. The earliest quartz–K feldspar alteration and veins are barren, whereas approximately 60% of the Cu reserves is associated with slightly later quartz–biotite–anhydrite alteration. Barren assemblages are related to irregular quartz (–K feldspar ± anhydrite) veins, which are truncated by the X porphyry. Cu sulfide-bearing assemblages are associated with discontinuous chalcopyrite (± biotite) and continuous quartz–anhydrite–chalcopyrite (± molybdenite) veins. Deposition of Cu–Mo with abundant anhydrite occurred during or between emplacement of closely related porphyries from high temperature magmatically-derived fluids, and was probably caused by the disproportionation of SO 2.

In situ quantitative analysis of individual H 2O–CO 2 fluid inclusions by laser Raman spectroscopy

Raman spectral parameters for the Raman ν 1 (1285 cm − 1 ) and 2 ν 2 (1388 cm − 1 ) bands for CO 2 and for the O–H stretching vibration band of H 2O (3600 cm − 1 ) were determined in H 2O–CO 2 fluid inclusions. Synthetic fluid inclusions containing 2.5 to 50 mol% CO 2 were analyzed at temperatures equal to or greater than the homogenization temperature. The results were used to develop an empirical relationship between composition and Raman spectral parameters. The linear peak intensity ratio (IR = ICO 2/(ICO 2 + IH 2O)) is related to the CO 2 concentration in the inclusion according to the relation: Mole % C O 2 = e − 3.959 IR 2 + 8.0734 IR where ICO 2 is the intensity of the 1388 cm − 1 peak and IH 2O is the intensity of the 3600 cm − 1 peak. The relationship between linear peak intensity and composition was established at 350 °C for compositions ranging from 2.5 to 50 mol% CO 2. The CO 2–H 2O linear peak intensity ratio (IR) varies with temperature and the relationship between composition and IR is strictly valid only if the inclusions are analyzed at 350 °C. The peak area ratio is defined as AR = ACO 2/(ACO 2 + AH 2O), where ACO 2 is the integrated area under the 1388 cm − 1 peak and AH 2O is the integrated area under the 3600 cm − 1 peak. The relationship between peak area ratio (AR) and the CO 2 concentration in the inclusions is given as: Mole % C O 2 = 312.5 AR The equation relating peak area ratio and composition is valid up to 25 mol% CO 2 and from 300 to 450 °C. The relationship between linear peak intensity ratio and composition should be used for inclusions containing ≤ 50 mol% CO 2 and which can be analyzed at 350 °C. The relationship between composition and peak area ratios should be used when analyzing inclusions at temperatures less than or greater than 350 °C (300–450) but can only be used for compositions ≤ 25 mol% CO 2. Note that this latter relationship has a somewhat larger standard deviation compared to the intensity ratio relationship. Calibration relationships employing peak areas for both members of the Fermi diad ( ν 1 at 1285 cm − 1 and 2 ν 2 at 1388 cm − 1 ) were slightly poorer than those using only the 2 ν 2 (1388 cm − 1 ) member owing to interference from quartz peak at approximately 1160 cm − 1 . The technique has been applied to natural low-salinity H 2O–CO 2 inclusions from the Butte, Montana, porphyry copper–molybdenum deposit. Carbon dioxide concentrations obtained range from below detection to 4.2 mol% CO 2, and are in good agreement with concentrations determined previously based on microthermometric and petrographic observations.

HYDROTHERMAL TRANSPORT AND DEPOSITION OF RHENIUM UNDER SUBCRITICAL CONDITIONS REVISITED

Data on the solubility of Re metal in subcritical hydrothermal solutions presented in Xiong and Wood (2001) have been reinterpreted assuming that the following reaction controlled dissolved Re concentrations: ReO2( s ) 2H2O( l ) ↔ Re(OH)4( aq ). The formation of ReO2( s ) on the surface of Re metal at the conditions of the previous experiments was demonstrated conclusively in a new experiment using X-ray photoelectron spectroscopy (XPS). The temperature dependence (200°–25°C) of the equilibrium constant for the above reaction at − 4700 ± 760 infinite dilution can be expressed as \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathit{K} = \frac{{-}4700 {\pm} 760}{\mathit{T}} + 6.2 {\pm} 2.0(2{\sigma})\) \end{document}. These new equilibrium constants predict that metallic rhenium, ReO2( s ), and ReS2( s ) have much lower solubilities than those implied in Xiong and Wood (2001). Based upon the new equilibrium constants, the free energy of formation, the enthalpy of formation, and entropy at the reference state (298.15 K and 1 bar) for the neutral rhenium species, Re(OH)4( aq ) (also alternatively formulated as ReO(OH)2( aq )), are derived in this study. Based on derived equilibrium constants at 25°C for dissolution of ReS2( s ) as Re(OH)4( aq ), we predict that rhenium can be enriched in the reduced zone in supergene environments in porphyry copper-molybdenum deposits.

Laramide Porphyry Cu-Mo Mineralization in Northern Mexico: Age Constraints from Re-Os Geochronology in Molybdenite

Twenty-five new Re-Os molybdenite ages for nine porphyry copper-molybdenum deposits from northern Mexico constrain the timing of mineralization and the longevity of porphyry systems in this region. The ages of all the deposits are between 50 and 61 Ma (i.e., Paleocene to early Eocene) and are associated with the Laramide orogeny. The oldest deposits are those from the Cananea district and include the El Alacran prospect (~61 Ma), the Maria deposit (60 Ma), the current Cananea mine, and La Colorada breccia (~59 Ma). The age of mineralization at Cumobabi also is 59 Ma, and it was followed by the emplacement of deposits at Suaqui Verde and Cuatro Hermanos at about 57 to 56 Ma. The Malpica prospect, the southernmost porphyry copper prospect in western Mexico, was emplaced at 54 Ma. The La Caridad deposit in Nacozari and the El Creston prospect both have Re-Os molybdenite ages of 54 Ma. The Tameapa prospect has a protracted hydrothermal mineralization history with multiple molybdenite mineralization events at ~57, 52 to 53, and 50 Ma. Total Re and 187 Os concentrations for molybdenites range from 10,424 to 26 ppm and from 6,641 to 14 ppb, respectively. The deposit with the highest Re and Os concentrations is El Alacran, and the lowest concentrations are found in El Creston. The ages determined support the formation of porphyry copper deposits in northern Mexico during the Laramide orogeny. In general, the ages of porphyry copper deposits in the North American province range from ~76 Ma at Bagdad, Arizona, to ~50 Ma at Tameapa, Sinaloa. The ages also show that porphyry copper mineralization occurred continuously between these two dates, with two main episodes at ~60 Ma (Cananea district, Mexico, and Sierrita and Copper Creek, United States) and at ~54 Ma (La Caridad, El Creston, Malpica in Mexico and Morenci, United States).

Mineralogical and Isotopic Zonation in the Sur-Sur Tourmaline Breccia, Rio Blanco-Los Bronces Cu-Mo Deposit, Chile: Implications for Ore Genesis

The Sur-Sur tourmaline breccia is located in the southeast part of the Rio Blanco-Los Bronces porphyry copper- molybdenum deposit, central Chile. The breccia hosts approximately one-quarter of the total resource of 57 Mt of fine copper at Rio Blanco. The breccia is hosted within, and contains altered clasts of, granodiorite from the 12 to 8 Ma San Francisco batholith, which intruded a sequence of Miocene volcanic and volcaniclastic rocks. A series of weakly mineralized to barren felsic porphyries cut the breccia and indicate a minimum age of approximately 6 Ma for mineralization at Sur-Sur. The Sur-Sur breccia dike is at least 3 km long, 0.2 km wide, and has a vertical extent of at least 1 km. The breccia has been cemented by early biotite and anhydrite at depth and by tourmaline and specularite at higher altitudes. These early-formed cements have been overgrown and in some cases replaced by chalcopyrite, magnetite, pyrite, and quartz. Mineralogical zonation in the breccia includes a transition from biotite cement and related biotite alteration upward to tourmaline cement and quartz-sericite-tourmaline alteration at approximately 3,000-m elevation. Iron-oxide minerals are also zoned, with a transition upward from a magnetite-dominated zone below 3,330 m to a specularite-dominated zone above 3,600 m. Pyrite is the dominant sulfide at altitudes above 4,000 m. Secondary liquid-rich, vapor-rich, and hypersaline fluid inclusions are preserved in quartz and tourmaline cement. Measured homogenization temperatures are mostly between 300 degrees and 450 degrees C, and salinities range from 0 to 69 wt percent NaCl equiv. Sulfur isotope compositions of sulfide cement range from -4.1 to +2.7 per mil. The lowest delta 34S(sulfide) values are in samples from between 3,700- and 4,000-m elevation, where they correspond to the highest copper grades in the tourmaline breccia. This high-grade zone also contains abundant specularite (locally replaced by magnetite). Modeling of sulfate-sulfide equilibrium indicate that approximately 150 degrees C of cooling over a vertical interval of 100 m would be required to account for the zonation of sulfide isotope compositions at Sur-Sur, making conductive cooling an unlikely ore-forming mechanism. Measured 206Pb/204Pb values of lead in anhydrite cement in the Sur-Sur tourmaline breccia and the Rio Blanco magmatic breccia range from 17.558 to 18.479. 207Pb/204Pb values range from 15.534 to 15.623, and 208Pb/204Pb values range from 37.341 to 38.412. The lead in anhydrite is considerably less radiogenic than that indicated by values obtained previously for lead in sulfide ores and igneous host rocks at Rio Blanco-Los Bronces. The source of lead in anhydrite must have been from rocks external to the main magmatichydrothermal system, probably the Precordilleran basement. A magmatic-hydrothermal explosion from a deep-seated crystallizing intrusion triggered breccia formation at Sur-Sur. Hydrostatic pressures catastrophically exceeded lithostatic load plus the tensile strength of the confining granodiorite, leading to widespread brecciation and subsequent invasion by large volumes of magmatic gas and hypersaline brine. The low-density gas phase (carrying H2O, SO2, HCl, and B2O3) separated physically from the dense copper-bearing brine and flushed through the breccia column first, where it condensed into ground waters of uncertain derivation. Anhydrite, specularite, and tourmaline were deposited from this lowsalinity, acidic, oxidized hybrid solution. Subsequent upwelling of magmatic-hydrothermal brine resulted in sulfide deposition. High-grade copper deposition is interpreted to have occurred in response to mixing of the oxidized, acidic water with the copper-bearing magmatic-hydrothermal brine.