Hydrothermal evolution of Daraloo porphyry copper deposit, Iran: evidence from fluid inclusions

The Daraloo field is located in the southeast of Iran (Kerman province). It is associated with Oligomiocene diorite/granodiorite to quartz monzonite stocks. Copper mineralization is basically relevant to potassic and phyllic alteration zones. Petrographic and geologic studies imply that mineralization is restricted to two major parts locating in the center and east of district. The larger central mineralization has a northwest–southeast trend perpendicular to the smaller one. Hydrothermal ore fluid formation occurred in relatively deep levels thereafter faulting and fracturing provided appropriate conduits to ascend fluids through shallower depths. Early hydrothermal alteration produced a confined potassic assemblage in the central and eastern parts of the stock. Two main fluid inclusion groups in relationship with alteration ore fluids have been identified. They are liquid-rich inclusions containing solid phases, with high temperatures (257°C to 554°C) and high salinities (31 to 67 wt.% NaCl equiv.), and vapor-rich inclusions with high temperatures and low salinities without any solid phases. These magmatic source fluids are responsible for boiling and also potassic and phyllic alteration zone. They also resulted in the formation of quartz groups I and II veins and chalcopyrite deposition. Propylitic alteration is attributed to a Ca-rich meteoric fluid. Inclusions originated from this fluid are liquid-rich having low temperatures (161°C to 269°C) and low salinities (1 to 13 wt.% NaCl). Mixing descending meteoric water with magmatic fluids reduces considerably the salinity of magmatic fluid. Mixing is also the impetus of leaching copper from potassic to the phyllic zone. It is possible to conclude that all these procedures are controlled by the main faults of district having NW–SE trend. Two fundamental events affecting the mineralization are cooling ore-bearing fluids and magnetite (±pyrite) emplacement. The latter one is formed in potassic and phyllic alteration zone in which copper-bearing fluids have interaction with magnetite minerals and so chalcopyrite minerals have been formed nearby magnetites. Temperature and pressure of hydrothermal fluid differentiation could be applied as a predictive tool to discriminate between barren and productive copper porphyry deposits. A simple comparison of temperature and pressure variations between Daraloo deposit and other copper porphyry deposits located in the same belt of Iran (Sahand-Bazman belt) illuminates that Daraloo system has high range of pressure implying deeper exsolution of hydrothermal fluid. On the other hand, economic mineralization has direct relationship with temperature range of orthomagmatic fluids so that if a deposit has a wide range of high temperature fluids, it could be inferred as a barren deposit. In conclusion, it could be inferred that Daraloo district can be categorized as a sub-economic porphyry deposit. On the other hand, restricted formation of chalcopyrite and the other copper-bearing minerals besides large amounts of magnetite and pyrite can approve obviously the low grade of mineralization in Daraloo district.     

Hydrothermal evolution of Darrehzar porphyry copper deposit,Iran: evidence from fluid inclusions

The Darrehzar porphyry Cu-Mo deposit is located in Southwestern Iran (～70 km southwest of Kerman City). The porphyries occur as Tertiary quartz-monzonite stocks and dikes, ranging in composition from microdiorite to diorite and granodiorite. The Darrehzar stock is highly altered, and even in the outermost part of the intrusion, it is not possible to find completely fresh rock. Surface weathering was developing ferrous Fe-rich lithologic units in leached zone and concentrated copper minerals in supergene zone. Unlike eastern areas which do not account for deep faults, the supergene zone is well developed in western areas with maximum of 118 m thickness. Hydrothermal alteration and mineralization at Darrehzar are centered on the stock and were broadly synchronous with its emplacement. Early hydrothermal alteration was dominantly potassic and propylitic, and was followed by later phyllic and argillic alteration. The hydrothermal system involved both magmatic and meteoric water and boiled extensively. Copper mineralization was accompanied by both potassic and phyllic alteration. Four main vein groups have been identified: (I) quartz?+?pyrite?±?molybdenite?±?anhydrite?±?K-feldspar?±?chalcopyrite?±?bornite?±?Cu and Fe oxidic minerals (peripheral); (II) quartz?+?chalcopyrite?+?pyrite?+?molybdenite; (III) quartz?+?pyrite?±?calcite?±?chalcopyrite?±?anhydrite (gypsum); and (IV) quartz or calcite, gypsum or ± pyrite. Based on abundance, nature, and phases number observed at room temperature, three types of fluid inclusions are typically observed in these veins: (1) vapor-rich, (2) liquid-rich, and (3) multi-phase. Early hydrothermal alteration was caused by high temperature, high salinity orthomagmatic fluid and produced a potassic assemblage. Phyllitic alteration was caused by high salinity and lower temperature orthomagmatic fluid. Magmatic and meteoric water mixture was developed in the peripheral part of the stock and caused propylitic alteration which is attributed to a liquid-rich, lower temperature.     

Geology and Re-Os Geochronology of Mineralization of the Miduk Porphyry Copper Deposit, Iran

The Miduk porphyry copper deposit is located in Kerman province, 85 km northwest of the Sar Cheshmeh porphyry copper deposit, Iran. The deposit is hosted by Eocene volcanic rocks of andesitic–basaltic composition. The porphyry‐type mineralization is associated with two Miocene calc‐alkaline intrusive phases (P1 and P2, respectively). Five hypogene alteration zones are distinguished at the Miduk deposit, including magnetite‐rich potassic, potassic, potassic–phyllic, phyllic and propylitic. Mineralization occurs as stockwork, dissemination and nine generations (magnetite, quartz–magnetite, barren quartz, quartz‐magnetite‐chalcopyrite‐anhydrite, chalcopyrite–anhydrite, quartz‐chalcopyrite‐anhydrite‐pyrite, quartz‐molybdenite‐anhydrite ± chalcopyrite ± magnetite, pyrite, and quartz‐pyrite‐anhydrite ± sericite) of veinlets and veins. Early stages of mineralization consist of magnetite rich veins in the deepest part of the deposit and the main stage of mineralization contains chalcopyrite, magnetite and anhydrite in the potassic zone. The high intensity of mineralization is associated with P2 porphyry (Miduk porphyry). Based on petrography, mineralogy, alteration halos and geochemistry, the Miduk porphyry copper deposit is similar to those of continental arc setting porphyry copper deposits. The Re‐Os molybdenite dates provide the timing of sulfide mineralization at 12.23 ± 0.07 Ma, coincident with U/Pb zircon ages of the P2 porphyry. This evidence indicates a direct genetic relationship between the Miduk porphyry stock and molybdenite mineralization. The Re‐Os age of the Miduk deposit marks the main stage of magmatism and porphyry copper formation in the Central Iranian volcano‐plutonic belt.     

The Bolcana Cu–Au ore deposit (Metaliferi Mountains,Romania): first data on the alteration and related mineralisation

The Bolcana ore deposit (Metaliferi Mountains, western Romania) is a porphyry ore deposit with associated epithermal veins. On the basis of different parageneses, four alteration types were distinguished: potassic, phyllic, argillic and propylitic. The mineralogical and geochemical data and estimated crystallisation temperatures of alteration minerals indicate an evolution of the system from an early period of porphyry type mineralisation (Cu+Au) to a late period of low-sulphidation epithermal mineralisation (Au+base metal). To cite this article: V. Milu et al., C. R. Geoscience 335 (2003).     

The Batu Hijau porphyry copper-gold deposit, Sumbawa Island, Indonesia

The Batu Hijau porphyry Cu---Au deposit lies in southwest Sumbawa Island, Indonesia. It is a world-class porphyry Cu deposit in an island are setting, and is typical of this deposit type in most features, including igneous association, morphology, hydrothermal alteration and mineralisation style.The region was not previously recognised as a porphyry Cu province; disseminated Cu sulphides were first recognised in float samples in southwest Sumbawa in 1987. Associated stream sediment sampling identified a broad area of anomalous Au and Cu in an area of greater than 5 km² around Batu Hijau, including 169 ppb Au in BLEG samples and 580 ppm Cu in stream silts 1 km from the deposit. Mineralisation in bedrock at surface contains > 0.1 wt % Cu and > 0.1 ppm Au over an area of 0.6 km × 1.2 km, including a zone 300 m × 900 m containing > 0.3 wt % Cu. Areas with elevated Mo (> 30 ppm) form a distinctive annulus around this Cu-rich zone.Batu Hijau mineralisation is hosted in a tonalite intrusive complex, and diorite and metavolcanic wallrocks. There are no post-mineralisation igneous intrusions or breccia pipes within the deposit. The main tonalite intrusion forms a stock in the centre of the deposit, where it generally displays intensely pervasive potassic (biotite with magnetite-quartz) alteration and hosts most of the higher grade mineralisation. Younger tonalite dykes intruding the centre of this stock are generally less altered and mineralised than the older tonalite.The core zone of potassic alteration grades outward into extensive propylitic alteration (chlorite-epidote), with both variably overprinted by widespread fracture controlled intermediate argillic alteration (sericite-chlorite), and minor phyllic (sericite-pyrite) and sodic (albite) alteration. Argillic (sericite-kaolinite) and advanced argillic (kaolinite-alunite-pyrophyllite) assemblages occur near surface.Copper and Au grades within the orebody show a positive correlation with quartz stockwork intensity, although disseminated Cu sulphides are also common. Chalcopyrite and bornite are the principle hypogenal minerals, with minor chalcocite. Oxidation extends to a depth of 5 m to 85 m below surface across the deposit, and is underlain by weak supergene mineralisation. Drill testing of the deposit down to 650 m below surface reveals a single cylindrical to conical orebody of 334 million tonnes grading 0.8 wt % Cu and 0.69 gm per tonne Au; the depth extent of mineralisation is unknown.     

Hydrothermal fluid geochemistry at the Chah-Firuzeh porphyry copper deposit,Iran: Evidence from fluid inclusions

The Chah-Firuzeh porphyry copper deposit is located in 35 km north of Shahre Babak (Kerman province). It is associated with granodioriteic intrusive of Miocene age which intruded Eocene volcanosedimentary rocks. Copper mineralization was accompanied by both potassic and phyllic alteration. Field observations and petrographic studies demonstrate that the emplacement of Chah-Firuzeh pluton took place in several intrusive pulses, each with associated hydrothermal ore fluid formation that was also associated with hydrostatic pressure increasing respect to that of lithostatic pressure (and fracturing development-relative boiling) by circulated fluid. Copper is concentrated as a very early hydrothermal mineralized phase in the evolution of the hydrothermal system. Early hydrothermal alteration produced a potassic assemblage (orthoclase–biotite) in the central deep part of the stock. Alteration ore fluids could be classify into two groups of liquid-reach, containing solid phases, high temperature (390 to 500 °C) high salinity (more than 60 wt.% NaCl equiv.) and gas-rich, high temperature (311 to 570 °C), no solid phase and with low salinities. These magmatic source fluids illustrate sever boiling process and also are the responsible for the both potassic alteration, quartz group I and II veins and chalcopyrite deposition. Propylitic alteration occurred by the liquid-rich, low temperature (241 to 390 °C) and Ca-rich fluid with meteoric origin. Continuous decreasing temperature let the meteoric water diffusion into the system, mixed with magmatic fluids and descending the salinities down to the 1 wt.% NaCl equiv. and leaching the Cu from vein groups II and III by sever thermodynamic anarchies from potassic to the phyllic alteration zones. Phyllic alteration and copper leaching resulted from the inflow of oxidized and acidic meteoric waters with decreasing temperature of the system followed by the incursion of this fluid into and its convection in upper part of the system. A late episode of boiling occurred in the apical the phyllic zone, and was associated with significant copper deposition. Based on the field observation on sharp alteration and related mineralization, it is possible to conclude that all these procedures have been controlled by local faults that could be active even before the pluton injection. These faults and the new form ones (which have been formed after injection), could crash the hosted rocks, and act as physical dams to restrict and limit the mineralization in special strikes and zones within the Cah-Firuzeh ore deposit.     

Geology and genesis of Variscan porphyry-style gold mineralization, Petráčkova hora deposit, Bohemian Massif, Czech Republic

A large number of Variscan mesothermal gold deposits are located in the central part of the Bohemian Massif, close to the Central Bohemian Plutonic Complex. The Petrá)kova hora deposit has many features that distinguish it from other deposits in the region and suggest its mineralization is closely related to the late magmatic processes associated with the Petrá)kova hora granodiorite. The gold ores occur as sheeted arrays of quartz veins and veinlets hosted by the small Petrá)kova hora granodiorite stock. Gold is found mainly as free grains of >900 fineness, and is accompanied by abundant pyrrhotite and chalcopyrite, and accessory pyrite, arsenopyrite, loellingite, and molybdenite. Molybdenite from the Petrá)kova hora deposit has been dated by the Re-Os method at 344.4DŽ.8 Ma. Hydrothermal alteration in the Petrá)kova hora deposit exhibits a distinct temporal paragenesis. Selectively pervasive, early K-alteration and silicification are the oldest hydrothermal phases. These were followed by early quartz veins (Q₁ to Q₄) that contain most of the gold mineralization. Late quartz veins (Q₅) and fracture-controlled silicification are gold-poor or barren. Barren calcite veins are the youngest hydrothermal product. Extensive low-temperature, meteoric-water dominated alteration, as is typical of classic porphyry deposits, is absent. However, the lower '¹⁸O whole rock values for Petrá)kova hora granodiorite and aplite (+2.4 to +5.1‰ SMOW) compared to other intrusions in the region reflect either interaction with isotopically light external fluids or magma assimilation of small volumes of hydrothermally altered country rock. The '¹⁸O isotopic compositions for quartz, scheelite and hornblende (7.7 to 13.4‰ SMOW) and the '³⁴S compositions for sulfide minerals (-1 to +3.5‰ CDT) from early, gold-rich quartz veins indicate formation at high temperatures (590 to 400 °C) from fluids with a magmatic isotopic signature ('¹⁸O_FLUID of 5.7 to 7.2‰). Fluids related to late quartz veins (Q₅) suggest the presence of a significant component of non-magmatic water ('¹⁸O_FLUID: +2.5 to +4.0‰). The '³⁴S values of post-Q₅ sulfide minerals (-4.5 to -3.5‰) reflect at least partial derivation of late-stage sulfur from a source external to the intrusions. Aqueous, aqueous-carbonic and nitrogen-bearing fluid inclusions were identified in hydrothermal and igneous quartz, with the aqueous inclusions being the most common. In hydrothermal vein quartz, the salinity of primary aqueous inclusions falls into ranges 6 to 23 and 33 to 41 equiv. wt% NaCl; in igneous quartz, populations in salinity were observed between 5 to 16, 35 to 40 and 62 to 70 equiv. wt% NaCl. The salt component of these fluids is best, and minimally, approximated by the NaCl-KCl-CaCl₂ system. Low- and high-salinity aqueous-carbonic inclusions are accessory in many of the analyzed samples. Three large successive pulses of fluids are recognized. Each pulse begins with a high-salinity (>30 equiv. wt% NaCl) magmatic fluid and evolves toward a lower salinity (~5 equiv. wt% NaCl) fluid. Data suggest that external (meteoric?) water(s) were significant for only the third fluid pulse, which formed the late Q₅ quartz veins and the calcite veins. Polyphase fluid inclusions hosted by igneous quartz of the Petrá)kova hora granodiorite indicate minimum trapping conditions of about 3 kbar and 550 °C. The gold-rich Q₁ to Q₄ veins may have formed along a quasi-isobaric cooling path at 2.5 to 1.5 kbar and 590 to 400 °C. This was followed by uplift, and formation of late Q₅ quartz veins (0.5 to 1.5 kbar; ~300 °C) and post-ore calcite veins (<0.5 kbar; 100 to 140 °C). The characteristics of the Petrá)kova hora deposit suggest that it may represent a position intermediate between intrusion-related gold systems (e.g., Fort Knox deposit, Alaska) and gold-rich, copper-poor porphyry deposits (e.g., Maricunga Belt in Chile). As such, the Petrá)kova hora deposit might be an example of the reduced gold sub-type of porphyry deposit.     

Rosia Poieni copper deposit,Apuseni Mountains,Romania: advanced argillic overprint of a porphyry system

The Rosia Poieni deposit is the largest porphyry copper deposit in the Apuseni Mountains, Romania. Hydrothermal alteration and mineralization are related to the Middle Miocene emplacement of a subvolcanic body, the Fundoaia microdiorite. Zonation of the alteration associated with the porphyry copper deposit is recognized from the deep and central part of the porphyritic intrusion towards shallower and outer portions. Four alteration types have been distinguished: potassic, phyllic, advanced argillic, and propylitic. Potassic alteration affects mainly the Fundoaia subvolcanic body. The andesitic host rocks are altered only in the immediate contact zone with the Fundoaia intrusion. Mg-biotite and K-feldspar are the main alteration minerals of the potassic assemblage, accompanied by ubiquitous quartz; chlorite, and anhydrite are also present. Magnetite, pyrite, chalcopyrite and minor bornite, are associated with this alteration. Phyllic alteration has overprinted the margin of the potassic zone, and formed peripheral to it. It is characterized by the replacement of almost all early minerals by abundant quartz, phengite, illite, variable amounts of illite-smectite mixed-layer minerals, minor smectite, and kaolinite. Pyrite is abundant and represents the main sulfide in this alteration zone. Advanced argillic alteration affects the upper part of the volcanic structure. The mineral assemblage comprises alunite, kaolinite, dickite, pyrophyllite, diaspore, aluminium-phosphate-sulphate minerals (woodhouseite-svanbergite series), zunyite, minamyite, pyrite, and enargite (luzonite). Alunite forms well-developed crystals. Veins with enargite (luzonite) and pyrite in a gangue of quartz, pyrophyllite and diaspore, are present within and around the subvolcanic intrusion. This alteration type is partially controlled by fractures. A zonal distribution of alteration minerals is observed from the centre of fractures outwards with: (1) vuggy quartz; (2) quartz + alunite; (3) quartz + kaolinite ± alunite and, in the deeper part of the argillic zone, quartz + pyrophyllite + diaspore; (4) illite + illite-smectite mixed-layer minerals ± kaolinite ± alunite, and e) chlorite + albite + epidote. Propylitic alteration is present distal to all other alteration types and consists of chlorite, epidote, albite, and carbonates. Mineral parageneses, mineral stability fields, and alteration mineral geothermometers indicate that the different alteration assemblages are the result of changes in both fluid composition and temperature of the system. The alteration minerals reflect cooling of the hydrothermal system from >400 °C (biotite), to 300–200 °C (chlorite and illite in veinlets) and to lower temperatures of kaolinite, illite-smectite mixed layers, and smectite crystallization. Hydrothermal alteration started with an extensive potassic zone in the central part of the system that passed laterally to the propylitic zone. It was followed by phyllic overprint of the early-altered rocks. Nearly barren advanced argillic alteration subsequently superimposed the upper levels of the porphyry copper alteration zones. The close spatial association between porphyry mineralization and advanced argillic alteration suggests that they are genetically part of the same magmatic-hydrothermal system that includes a porphyry intrusion at depth and an epithermal environment of the advanced argillic type near the surface.Editorial handling: B. Lehmann     

五子骑龙矿床——被改造的斑岩铜矿上部带

五子骑龙矿床产于紫金山矿田的一个早白垩世火山管道旁侧。火山管道中充填的英安斑岩向深部逐渐相变为花岗闪长斑岩。由于后期断裂的破坏，该花岗闪长斑岩及其矿化系统被上冲到与五子骑龙矿床相邻的中寮矿床近地表位置，从而形成斑岩型铜矿床－中寮矿床。五子骑龙矿床中，环绕英安斑岩发育明矾石化、迪开石化、埃洛石化和红柱石化蚀变，这些蚀变是改造并叠加早期绢英岩化蚀变的结果。其铜矿石中的铜蓝、硫砷铜矿和蓝辉铜矿，也经常交     

The michiquillay porphyry copper deposit

Michiquillay is a mineralized intrusive quartz monzonite porphyry displaying typical porphyry copper alteration zones as found in metallized intrusives of that composition. From the interior outward these are the phyllic, argillic and propylitic zones. The potassic zone is not exposed at the surface. The intrusion and the center of mineralization coincide with the intersection of a major transverse fault and a cross fault. Mineralization appears dominantly to occur in fractures which may be related to each of these major structures, and is ascribed in origin to simultaneous movement on each fault during the period of hydrothermal activity. The stockwork developed at the fault intersection, and which is the locus of the ore body, fades as distance is gained away from its center. Coincidentally, intensity of mineralization also weakens.     

Genesis of the Fuxing porphyry Cu deposit in Eastern Tianshan,China: Evidence from fluid inclusions and C–H–O–S–Pb isotope systematics

The Fuxing porphyry Cu deposit is a recently discovered deposit in Eastern Tianshan, Xinjiang, northwestern China. The Cu mineralization is associated with the Fuxing plagiogranite porphyry and monzogranite, mainly presenting as various types of hydrothermal veins or veinlets in alerted wall rocks, with potassic, chlorite, phyllic, and propylitic alteration developed. The ore-forming process can be divided into four stages: stage I barren quartz veins, stage II quartz–chalcopyrite–pyrite veins, stage III quartz–polymetallic sulfide veins and stage IV quartz–calcite veins. Four types of fluid inclusions (FIs) can be distinguished in the Fuxing deposit, including hypersline (H-type), vapor-rich two-phase (V-type), liquid-rich two-phase (L-type), and trace amounts of pure vapor inclusions (P-type), but only the stage I quartz contains all types of FIs. The stages II and III quartz have two types of FIs, with exception of H- and P-types. In stage IV quartz minerals, only the L-type inclusions can be observed. The FIs in quartz of stages I, II, III and IV are mainly homogenized at temperatures of 357–518 °C, 255–393 °C, 234–322 °C and 145–240 °C, with salinities of 1.9–11.6 wt.% NaCl equiv., 1.6–9.6 wt.% NaCl equiv., 1.4–7.7 wt.% NaCl equiv. and 0.9–3.7 wt.% NaCl equiv., respectively. The ore-forming fluids of the Fuxing deposit are characterized by high temperature, moderate salinity and relatively oxidized condition. Carbon, hydrogen and oxygen isotopic compositions of quartz indicate that the ore-forming fluids were gradually evolved from magmatic to meteoric in origin. Sulfur and lead isotopes suggest that the ore-forming materials were derived from a deep-seated magma source. The Cu mineralization in the Fuxing deposit occurred at a depth of ~ 1 km, and the changes of oxygen fugacity, decompression boiling, and local mixing with meteoric water were most likely critical for the formation of the Fuxing Cu deposit.     

Metallogenesis in the Harlech Dome,North Wales: A fluid inclusion interpretation

A regional fluid inclusion study of Cu-Au (+Zn-Pb) mineralisation in the Harlech Dome area, North Wales, gives support to the concept of two distinct metallogenic episodes. The inclusion assemblages associated with the porphyry copper mineralisation at Coed-y-Brenin are consistent with a genetic model of early potassic-propylitic alteration overprinted by later phyllic alteration. High salinity fluids, normally characteristic of potassic alteration, are confined to the host rock quartz. The meteoric/hydrothermal system is closely linked to the emplacement of late-Cambrian diorites. Integrated fluid inclusion and mineralogical studies of the Gold-belt veins suggest that the mineralising fluids were probably dehydration waters released from weakly metamorphosed Cambrian and perhaps Precambrian sediments during hydraulic fracturing in a tensional zone at the close of the Caledonian orogeny. Localisation of economic concentrations of gold in veins at the level of the Clogau Formation is ascribed to a destabilisation of metal complexes caused by a change in fluid buffering from a pyrite-magnetite assemblage in the Lower Cambrian sediments to a pyrite-pyrrhotite-graphite assemblage in the Upper Cambrian sediments. Veining associated with the Coed-y-Brenin porphyry copper deposit and related breccia pipes can be distinguished from the copper-gold veins of the coextensive Dolgellau Gold-belt by the presence in the former of inclusions notably richer in CO₂. Furthermore the Gold-belt fluids have a distinctive low CO₂/CH₄+N₂+H₂ ratio.     

西藏尼木地区岗讲斑岩铜-钼矿床地质特征及锆石U-Pb年龄

岗讲铜-钼矿床位于冈底斯中段尼木矿田之中,是近年新发现的一个储量在大型以上的典型斑岩型铜-钼矿床。含矿岩体为复式岩体,其中铜、钼矿化主要产于黑云石英二长岩、石英二长斑岩和流纹-英安斑岩之中。热液蚀变类型有钾化、硅化、绢英岩化、绿泥石化和局部泥化,从岩体中心向外主要发育钾化带和绢英岩化带。矿体主要分布在钾化带与绢英岩化带叠加部位,矿区次生氧化富集带也比较发育。文中利用二次离子探针质谱(SIMS)对主要含矿岩体进行了锆石U-Pb定年研究,获得黑云石英二长岩和流纹-英安斑岩的结晶年龄分别为(14.73±0.13)Ma(MSWD=1.3,N=16)和(12.01±0.29)Ma(MSWD=2.3,N=8),与尼木矿田其他斑岩铜(钼)矿床含矿斑岩体的形成年龄基本一致,表明岗讲铜-钼矿床形成于印度-欧亚大陆板块碰撞后的伸展阶段。鉴于矿区缺失青磐岩化带,且钾化带主体已出露地表,因此该区的剥蚀深度至少应该在2～3 km,这与结合青藏高原的剥蚀速率(0.13～0.23mm/a)估算的剥蚀深度一致。     

Himalayan magmatism and porphyry copper–molybdenum mineralization in the Yulong ore belt, East Tibet

Summary ?The NW–SE-trending Yulong porphyry Cu–Mo ore belt, situated in the Sanjiang0 area of eastern Tibet, is approximately 400 km long and 35 to 70 km wide. Complex tectonic and magmatic processes during the Himalayan epoch have given rise to favorable conditions for porphyry-type Cu–Mo mineralization. Porphyry masses of the Himalayan epoch in the Yulong ore belt are distributed in groups along regional NW–SE striking tectonic lineaments. They were emplaced mainly into Triassic and Lower Permian sedimentary-volcanic rocks. K–Ar und U–Pb isotopic datings give an intrusion age range of 57–26 Ma. The porphyries are mainly of biotite monzogranitic and biotite syenogranitic compositions. Geological and geochemical data indicate that the various porphyritic intrusions in the belt had a common or similar magma source, are metaluminous to peraluminous, Nb–Y–Ba-depleted, I-type granitoids, and belong to the high-K calc-alkaline series. Within the Yulong subvolcanic belt a number of porphyry stocks bear typical porphyry type Cu–Mo alteration and mineralization. The most prominent porphyry Co–Mo deposits include Yulong, Malasongduo, Duoxiasongduo, Mangzong and Zhanaga, of which Yulong is one of the largest porphyry Cu (Mo) deposits in China with approximately 8 × 10⁶ tons of contained Cu metal. Hydrothermal alteration at Yulong developed around a biotite–monzogranitic porphyry stock that was emplaced within Upper Triassic limestone, siltstone and mudstone. The earliest alteration was due to the effects of contact metamorphism of the country rocks and alkali metasomatism (potassic alteration) within and around the porphyry body. The alteration of this stage was accompanied by a small amount of disseminated and veinlet Cu–Mo sulfide mineralization. Later alteration–mineralization zones form more or less concentric shells around the potassic zone, around which are distributed a phyllic or quartz–sericite–pyrite zone, a silicification and argillic zone, and a propylitic zone. Fluid inclusion data indicate that three types of fluids were involved in the alteration–mineralization processes: (1) early high temperature (660–420 °C) and high salinity (30–51 wt% NaCl equiv) fluids responsible for the potassic alteration and the earliest disseminated and/or veinlet Cu–Mo sulfide mineralization; (2) intermediate unmixed fluids corresponding to phyllic alteration and most Cu–Mo sulfide mineralization, with salinities of 30–50 wt% NaCl equiv and homogenization temperatures of 460–280 °C; and (3) late low to moderate temperature (300–160 °C) and low salinity (6–13 wt% NaCl equiv) fluids responsible for argillic and propylitic alteration. Hydrogen and oxygen isotopic studies show that the early hydrothermal fluids are of magmatic origin and were succeeded by increasing amounts of meteoric-derived convective waters. Sulfur isotopes also indicate a magmatic source for the sulfur in the early sulfide mineralization, with the increasing addition of sedimentary sulfur outward from the porphyry stock. Received August 29, 2001; revised version accepted May 1, 2002 Published online: November 29, 2002     

西藏玉龙铜矿床成矿斑岩的厘定及地质意义

位于青藏高原东缘的玉龙铜矿是我国最大的斑岩铜矿之一,其形成一致认为与矿区中心产出的二长花岗质复式斑岩体有关,但成矿与复式岩体的确切关系并不清楚。本文通过详细的野外地质填图,特别是矿床8号勘探线12个钻孔的重新编录,在复式岩体中识别出一套花岗斑岩岩枝,岩枝中不规则状石英-钾长石脉广泛发育,同时还见有单向固结结构、粗晶及细晶结构,这些特征表明该岩浆中的流体曾经发生过饱和。同时结合矿床高品位(0.6%,质量分数)铜矿化紧密围绕花岗斑岩分布、含矿脉体自花岗斑岩向外围逐渐由高温石英-钾长石A脉过渡为中低温石英-硫化物脉、热液蚀变自花岗斑岩向外由高温钾硅酸盐化过渡为中低温石英-绢云母化的规律,最终确定这套花岗斑岩为玉龙矿床的成矿斑岩。玉龙铜矿成矿斑岩的厘定,较好地解释了矿床矿化类型及金属的分布规律,为进一步深入理解矿床形成过程提供了帮助。     

安徽沙溪斑岩型铜金矿床成岩序列及成岩成矿年代学研究

沙溪矿床是长江中下游成矿带中典型的斑岩型铜金矿床,位于庐枞盆地北外缘、郯庐断裂内,矿床成岩成矿时代确定对该矿床成因研究及区域成矿规律的认识具有重要意义。在详细野外地质工作的基础上,采集沙溪矿床与成矿有关的主要岩浆岩样品(粗斑闪长玢岩、黑云母石英闪长玢岩、中斑石英闪长玢岩、细斑石英闪长玢岩和闪长玢岩)和与黄铜矿密切共生的辉钼矿,分别利用Cameca、LA-ICP-MS U-Pb和Re-Os同位素定年方法,获得矿床内主要岩浆岩的成岩年龄(130.60±0.97Ma、129.30±1.00Ma、127.10±1.50Ma、129.46±0.97Ma和126.7±2.1Ma)以及成矿年龄(130.0±1.0Ma),并重新厘定了沙溪岩体从早到晚岩浆的侵位序列。通过区域对比,提出长江中下游存在两阶段斑岩型铜金矿化,沙溪矿床为长江中下游成矿带第二阶段形成的斑岩型矿床,沙溪矿床的成岩成矿作用既不同于庐枞盆地,也不同于断隆区第一阶段的斑岩矿床,而是受郯庐断裂和长江断裂动力学演化联合作用的产物。     

Spectral characteristics of minerals in alteration zones associated with porphyry copper deposits in the middle part of Kerman copper belt,SE Iran

Visible near infrared and shortwave infrared (VNIR-SWIR, 350 to 2500 nm) reflectance spectra obtained from an analytical spectral device (ASD) have been used to define alteration zones adjacent to porphyry copper deposits (PCDs), in the central part of Kerman magmatic arc, SE Iran. The spectral analysis identified sericite, illite, halloysite, montmorillonite, dickite, kaolinite, pyrophyllite, biotite, chlorite, epidote, calcite, jarosite, and iron oxyhydroxides (e.g. hematite, goethite) of hydrothermal and supergene origin. Identified alteration zones are classified into six principal types namely phyllic, phyllic/propylitic, propylitic, potassic, argillic and advanced argillic. The iron oxide minerals in the oxidized zone were also identified using spectral analysis. Results of spectral analyses of samples are consistent with mineralogical data obtained from X-ray diffraction (XRD) and petrographic studies. Spectroscopic studies by ASD demonstrate that this tool is very useful for semi-quantitative and cost effective identification of different types of alteration mineral assemblages. Furthermore, it can provide a valuable tool for evaluating aerial distribution of alteration minerals while coupled with remote sensing data analysis.     

Late Miocene Magmatic-Hydrothermal Systems in the Jozankei-Zenibako District, Southwest Hokkaido, Japan

Abstract: Hydrothermal systems related to magmatic intrusions in the Jozankei-Zenibako district, southwest Hokkaido are examined, based on field observations, K-Ar ages, and alteration mineral assemblages. The study reveals five major magmat–ic–hydrothermal systems of Late Miocene in age, comprising Ogawa (9. 7 Ma), Jozankei (9. 5–9. 0 Ma), Otarunaigawa (8. 7 Ma), Asarigawa (8. 8 and 6. 7 Ma) and Hariusu (6. 7 Ma). The Ogawa system is related to granodiorite, and the Jozankei, Otarunaigawa and Asarigawa systems are related to quartz porphyry.
The Ogawa system includes potassic, sericitic, propylitic and advanced argillic alteration as well as base-metal mineralization, represented by the Toyotomi deposit. The Jozankei and Otarunaigawa systems lack significant potassic alteration, and are accompanied by sericitic and propylitic alteration. The Otarunaigawa system is associated with base-metal mineralization at Toyohiro and Inatoyo. The Asarigawa and Hariusu systems include advanced argillic and argillic alteration, as well as iron sulfide deposits. The presence of potassic alteration only in the Ogawa system is ascribed to deeper emplacement (˜3 km from the surface) of the intrusive magma. These systems formed in terrestrial environments that existed from ca. 11 Ma to 8. 5 Ma and after 7. 5 Ma in the district.
Age–data compilation shows that the major advanced argillic alteration events in southwest Hokkaido, including those in the Jozankei-Zenibako district, formed during the periods from 9. 7–6. 5 Ma and 3. 5–1. 5 Ma. These periods correspond to the timing of normal subduction of the Pacific plate beneath the Northeast Japan arc. Normal, in contrast to oblique, plate subduction is characterized by andesitic, polygenetic volcanism and associated advanced argillic alteration.     

Hydrothermal evolution of the Sar-Cheshmeh porphyry Cu–Mo deposit,Iran: Evidence from fluid inclusions

The Sar-Cheshmeh porphyry Cu–Mo deposit is located in Southwestern Iran (∼65 km southwest of Kerman City) and is associated with a composite Miocene stock, ranging in composition from diorite through granodiorite to quartz-monzonite. Field observations and petrographic studies demonstrate that the emplacement of the Sar-Cheshmeh stock took place in several pulses, each with associated hydrothermal activity. Molybdenum was concentrated at a very early stage in the evolution of the hydrothermal system and copper was concentrated later. Four main vein Groups have been identified: (I) quartz+molybdenite+anhydrite±K-feldspar with minor pyrite, chalcopyrite and bornite; (II) quartz+chalcopyrite+pyrite±molybdenite±calcite; (III) quartz+pyrite+calcite±chalcopyrite±anhydrite (gypsum)±molybdenite; (IV) quartz±calcite±gypsum±pyrite±dolomite. Early hydrothermal alteration produced a potassic assemblage (orthoclase-biotite) in the central part of the stock, propylitic alteration occurred in the peripheral parts of the stock, contemporaneously with potassic alteration, and phyllic alteration occurred later, overprinting earlier alteration. The early hydrothermal fluids are represented by high temperature (350–520 °C), high salinity (up to 61 wt% NaCl equivalent) liquid-rich fluid inclusions, and high temperature (340–570 °C), low-salinity, vapor-rich inclusions. These fluids are interpreted to represent an orthomagmatic fluid, which cooled episodically; the brines are interpreted to have caused potassic alteration and deposition of Group I and II quartz veins containing molybdenite and chalcopyrite. Propylitic alteration is attributed to a liquid-rich, lower temperature (220–310 °C), Ca-rich, evolved meteoric fluid. Influx of meteoric water into the central part of the system and mixing with magmatic fluid produced albitization at depth and shallow phyllic alteration. This influx also caused the dissolution of early-formed copper sulphides and the remobilization of Cu into the sericitic zone, the main zone of the copper deposition in Sar-Cheshmeh, where it was redeposited in response to a decrease in temperature.     

Lead isotope data from the Sar-Cheshmeh porphyry copper deposit,Iran

Lead isotope compositions of nine sulfide concentrates from ore samples from the Sar-Cheshmeh deposit are reported. They range from virtually unaltered granodiorite through varying degrees of potassic alteration to ores showing strong phyllic alteration (sericite veins). The samples without strong phyllic alteration have fairly uniform lead isotope compositions around ²⁰⁶Pb/²⁰⁴Pb=18.6, ²⁰⁷Pb/²⁰⁴Pb=15.6, and ²⁰⁸Pb/²⁰⁴Pb=38.7. Two samples with sericite veins have markedly more radiogenic lead. It is concluded that the fluid responsible for the potassic alteration and the associated mineralization was essentially magmatic, whereas convecting meteoric water from the country rock acted as a mineralizing solution during phyllic alteration. In the context of the plumbotectonics model, the deposit has a typical orogen signature intermediate between primitive and mature island-arc settings.