Boron in the Bolivian tin belt

Tourmaline alteration and high boron contents are typical features of the magmatic-hydrothermal systems of the Bolivian tin province. The average boron content in melt inclusions of quartz phenocrysts from tin porphyry systems is 225 ppm (1σ-variation range: 110–420 ppm; n=12) and suggests a magmatic boron input to the hydrothermal tin systems, and not shallow post-magmatic leaching of boron from pelitic country rocks. Boron data from melt inclusions correlate positively with cesium, rubidium and arsenic, and negatively with lithium, titanium and zirconium, and define magmatic fractionation trends. The generally high B, As, Cs and Li contents in melt inclusions suggest involvement of pelitic source lithologies undepleted in these fluid-mobile components, i.e. first-cycle metamorphic rocks. Magmatic fractionation modified the trace-element contents within a one-log-unit range. Bulk-rock Nd isotope data (ɛ_Nd−5 to −10) are in agreement with the dominantly intracrustal geochemical signature of the Bolivian tin porphyry systems, but also imply a variable but minor mantle input. The metallogeny of the tin belt is likely a consequence of intracrustal melting of Lower Paleozoic pelitic and slightly carbonaceous source material, combined with an extended magmatic evolution. The long-lived thermal preparation of the root zones of the silicic systems is provided by mafic magma which also leaves a chemical imprint in the form of the hybrid dacitic bulk composition of the tin porphyry systems. Received: 6 August 1998 / Accepted: 19 August 1999     

An intrusion-related origin for Cu–Au mineralization in iron oxide–copper–gold (IOCG) provinces

Major Cu–Au deposits of iron oxide–copper–gold (IOCG) style are temporally associated with oxidized, potassic granitoids similar to those linked to major porphyry Cu–Au deposits. Stable and radiogenic isotope evidence indicates fluids and ore components were likely sourced from the intrusions. IOCG deposits form over a range of crustal levels because CO₂-rich fluids separate from the magmas at higher pressures than in CO₂-poor systems, thereby, promoting partitioning of H₂O, Cl and metals to the fluid phase. At deep levels, the magma–fluid system cannot generate sufficient mechanical energy to fracture the host rocks as in porphyry systems and the IOCG deposits therefore form in a variety of fault-related structural traps where the magmatic fluids may mix with other fluids to promote ore formation. At shallow levels, the IOCG deposits form breccia and fracture-hosted mineralization styles similar to the hydrothermal intrusive breccias and sulphide vein systems that characterize many porphyry Cu–Au deposits. The fluids associated with IOCG deposits are typically H₂O–CO₂–salt fluids that evolve by unmixing of the carbonic phase and by mixing with fluids from other sources. In contrast, fluids in porphyry systems typically evolve by boiling of moderate salinity fluid to produce high salinity brine and a vapor phase commonly with input of externally derived fluids. These different fluid compositions and mechanisms of evolution lead to different alteration types and parageneses in porphyry and IOCG deposits. Porphyry Cu–Au deposits typically evolve through potassic, sericitic and (intermediate and/or advanced) argillic stages, while IOCG deposits typically evolve through sodic(–calcic), potassic and carbonate-rich stages, and at deeper levels, generally lack sericitic and argillic alteration. The common association of porphyry and IOCG Cu–Au deposits with potassic, oxidized intermediate to felsic granitoids, together with their contrasting fluid compositions, alteration styles and parageneses suggest that they should be considered as part of the broad family of intrusion-related systems but that they are typically not directly related to each other.     

江西会昌锡坑迳斑岩型锡矿床成矿系统发育特征与找矿模型

锡坑迳矿田位于南岭成矿带东段与武夷山成矿带交会部位,以早白垩世连续的岩浆喷发-侵入活动与多类型锡多金属成矿作用为特色。矿田内围绕似斑状花岗岩和花岗斑岩发育了岩背斑岩型、淘锡坝和矿背隐爆层间裂隙带型、苦竹岽和凤凰岽云英岩-破碎带蚀变岩型等大中型锡矿床。这些矿床的矿化-蚀变特征可与玻利维亚锡矿带、银岩、维拉斯托和洋滨等国内外斑岩型锡矿床类比,又独具特色,是研究斑岩型锡成矿系统发育特征与找矿模型的理想区域。文章在详细的野外地质调查基础上,系统总结了锡坑迳矿田内各类锡多金属矿化组合特征和蚀变结构,并对岩背矿床和淘锡坝矿床锡石开展了电子探针和LA-ICP-MS原位微区分析。研究结果显示,所有锡石样品均具有La、Pr、Gd和Tb的正异常、Ce与Eu的负异常、明显的Zr/Hf分馏和不规则的稀土元素配分模式,指示成矿热液早期阶段及锡石沉淀阶段经历了流体不相容。岩背锡石较淘锡坝锡石具有高的Ti/Zr和Ti/Sc比值,指示其更为靠近矿化中心。笔者研究认为,锡坑迳斑岩型锡成矿系统矿化类型包括细脉状、浸染状和细网脉状,围岩蚀变由早到晚、由成矿中心向外依次发育黄玉石英带、绿泥石-黄玉石英岩化带、绿泥石-绢云母化带和黏土化-碳酸盐化带。与斑岩型铜钼成矿系统相比,其成矿岩浆岩不仅有花岗斑岩,还有似斑状黑云母花岗岩,矿体在斑岩、花岗岩及上覆火山岩中均有赋存。相较于玻利维亚斑岩型锡成矿带发育的大面积石英-电气石化,锡坑迳斑岩成矿系统更富F,蚀变矿物中出现了大量黄玉、萤石和白云母等。对比国内外典型锡矿床的矿化-蚀变结构和锡石矿物学特征,文章建立了锡坑迳式斑岩型锡成矿系统的找矿模型。     

内蒙古维拉斯托锡多金属矿流体包裹体特征

大兴安岭锡矿带是中国北方唯一成型的锡多金属成矿带。新近发现的内蒙古维拉斯托锡多金属矿床位于大兴安岭南段,隶属中亚造山带东段的兴蒙造山带。该矿床为一典型的大型斑岩型热液脉型锡多金属矿床,矿区内锡矿化主要赋存于石英斑岩体顶部及其上部的石英脉中。矿床成矿阶段包括石英斑岩体内的滴状锡锌矿化阶段、石英斑岩体上部石英脉中的辉钼矿矿化阶段、石英锡石黑钨矿阶段和石英多金属硫化物阶段。流体包裹体研究结果显示：流体包裹体类型主要为气液两相包裹体,尤其是富液相包裹体,其次为含子矿物的三相包裹体。斑岩体内矿化阶段流体包裹体均一温度为324~333 ℃,盐度为6.5%~7.5% NaCleqv,密度为0.73~0.74 g/cm3;石英脉型矿化阶段包裹体均一温度为201~324 ℃,盐度为3.4%~9.9% NaCleqv,密度为0.73~0.92 g/cm3。包裹体显微测温分析结果显示该矿区成矿流体具有中高温、低盐度、中密度的特征。激光拉曼光谱分析表明,气液两相包裹体液相成分主要为H2O,气相成分主要有H2O、CO2和CH4。氢氧同位素研究结果表明该矿床石英斑岩体上部石英脉矿化阶段的成矿流体为岩浆水和大气降水混合来源,以岩浆水为主。岩浆流体与大气降水的混合以及流体演化中的降温过程是该矿床矿石沉淀的主要机制。     

与花岗质岩浆系统有关的石英脉型钨矿和斑岩型铜矿成矿流体特征比较

文中对比了与S型花岗岩有关的石英脉型钨矿和与I型（及少数A型）花岗岩类有关的斑岩型铜矿床的成矿流体特征。它们的共同点在于成矿流体都由岩浆流体演化而来,在后期逐渐有大气降水的加入。差异性在于：（1）石英脉型钨矿成矿流体主要属于中—中高温、中—中低盐度的NaCl-H2O±CO2体系,而斑岩型铜矿属于中高-高温、高盐度的Na...     

Examining potential genetic links between Jurassic porphyry Cu–Au ± Mo and epithermal Au ± Ag mineralization in the Toodoggone district of North-Central British Columbia,Canada

The Toodoggone district comprises Upper Triassic to Lower Jurassic Hazelton Group Toodoggone Formation volcanic and sedimentary rocks, which unconformably overlie submarine island-arc volcanic and sedimentary rocks of the Lower Permian Asitka Group and Middle Triassic Takla Group, some of which are intruded by Upper Triassic to Lower Jurassic plutons and dikes of the Black Lake suite. Although plutonism occurred episodically from ca. 218 to 191 Ma, the largest porphyry Cu–Au ± Mo systems formed from ca. 202 to 197 Ma, with minor mineralization occurring from ca. 197 to 194 Ma. Porphyry-style mineralization is hosted by small-volume (<1 km³), single-phase, porphyritic igneous stocks or dikes that have high-K calc-alkaline compositions and are comparable with volcanic-arc granites. The Fin porphyry Cu–Au–Mo deposit is anomalous in that it is 16 m.y. older than any other porphyry Cu–Au ± Mo occurrence in the district and has lower REEs. All porphyry systems are spatially restricted to exposed Asitka and Takla Group basement rocks, and rarely, the lowest member of the Hazelton Group (i.e., the ca. 201 Ma Duncan Member). The basement rocks to intrusions are best exposed in the southern half of the district, where high rates of erosion and uplift have resulted in their preferential exposure. In contrast, low- and high-sulfidation epithermal systems are more numerous in the northern half of the district, where the overlying Hazelton Group rocks dominate exposures. Cogenetic porphyry systems might also exist in the northern areas; however, if they are present, they are likely to be buried deeply beneath Hazelton Group rocks. High-sulfidation epithermal systems formed at ca. 201 to 182 Ma, whereas low-sulfidation systems were active at ca. 192 to 162 Ma. Amongst the studied epithermal systems, the Baker low-sulfidation epithermal deposit displays the strongest demonstrable genetic link with magmatic fluids; fluid inclusion studies demonstrate that its ore fluids were hot (>468°C), saline, and deposited metals at deep crustal depths (>2 km). Sulfur, C, O, and Pb isotope data confirm the involvement of a magmatic fluid, but also suggest that the ore fluid interacted with Asitka and Takla Group country rocks prior to metal deposition. In contrast, in the Shasta, Lawyers, and Griz-Sickle low-sulfidation epithermal systems, there is no clear association with magmatic fluids. Instead, their fluid inclusion data indicate the involvement of low-temperature (175 to 335°C), low-salinity (1 to 11 equiv. wt.% NaCl) fluids that deposited metals at shallow depths (<850 m). Their isotope (i.e., O, H, Pb) data suggest interaction between meteoric and/or metamorphic ore fluids with basement country rocks.     

新疆东准噶尔老鸦泉富碱花岗岩型锡矿床地质及成矿流体

老鸦泉碱性花岗岩位于新疆北部东准噶尔地区。老鸦泉碱性花岗岩体及其内卡姆斯特、干梁子锡矿床的矿石和岩石的岩矿鉴定、稀土元素以及流体包裹体的系统研究表明,老鸦泉碱性花岗岩及其内的花岗斑岩及含矿石英岩、云英岩化锡矿体、石英脉锡矿体,实际上是富碱花岗质岩浆逐渐分异演化的同源和最终产物,锡成矿流体为中-高温、低盐度。碱性岩浆晚期分异的大量气水热液富锡、富硅、富碱、富含F、Cl、SO²₄离子及离子团,其氧逸度高、酸度高、温度高,这种热液引起花岗岩体的硅化、云英岩化等自变质作用,在该作用中随温度、压力的降低及CH₄等还原性气体及CO₂气体的逃逸,改变了成矿流体的氧化-还原环境,流体向相对还原及碱性条件转化,在新的氧化还原、酸碱度界面条件下,其携带的锡的络合物不稳定而分解,锡沉淀成矿。     

The role of the Antofagasta–Calama Lineament in ore deposit deformation in the Andes of northern Chile

During the Late Jurassic–Early Oligocene interval, widespread hydrothermal copper mineralization events occurred in association with the geological evolution of the southern segment of the central Andes, giving rise to four NS-trending metallogenic belts of eastward-decreasing age: Late Jurassic, Early Cretaceous, Late Paleocene–Early Eocene, and Late Eocene–Early Oligocene. The Antofagasta–Calama Lineament (ACL) consists of an important dextral strike-slip NE-trending fault system. Deformation along the ACL system is evidenced by a right-lateral displacement of the Late Paleocene–Early Eocene metallogenic belts. Furthermore, clockwise rotation of the Early Cretaceous Mantos Blancos copper deposit and the Late Paleocene Lomas Bayas porphyry copper occurred. In the Late Eocene–Early Oligocene metallogenic belt, a sigmoidal deflection and a clockwise rotation is observed in the ACL. The ACL is thought to have controlled the emplacement of Early Oligocene porphyry copper deposits (34–37 Ma; Toki, Genoveva, Quetena, and Opache), whereas it deflected the Late Eocene porphyry copper belt (41–44 Ma; Esperanza, Telégrafo, Centinela, and Polo Sur ore deposits). These observations suggest that right-lateral displacement of the ACL was active during the Early Oligocene. We propose that the described structural features need to be considered in future exploration programs within this extensively gravel-covered region of northern Chile.     

新疆东准噶尔老鸦泉碱性岩及相关锡矿的岩石地球化学特征

老鸦泉富碱花岗岩杂岩体与侵入其中的富碱花岗斑岩岩体及云英岩型锡矿体、石英脉型锡矿体等REE配分曲线类似,均具有强烈的Eu亏损,它们的微量元素蛛网图等岩石地球化学特征也类似,是同源岩浆结晶分异演化的结果。锡矿体是老鸦泉富碱岩浆分异演化及以钠质为主的强烈碱交代自变质作用的最终产物。侵入于老鸦泉岩体内的花岗斑岩为锡矿体的直接围岩,它是岩浆结晶分异更晚期混入了更多地壳组分,并向酸性方向演化的产物,该花岗斑岩经自变质热液蚀变作用造成锡的富集并成矿。因此,碱性岩浆结晶分异晚期混有地壳组分,岩浆向酸性演化可能是碱性花岗岩形成锡矿的重要条件之一。     

Formation of the Vysoká–Zlatno Cu–Au skarn–porphyry deposit, Slovakia

The central zone of the Miocene Štiavnica stratovolcano hosts several occurrences of Cu–Au skarn–porphyry mineralisation, related to granodiorite/quartz–diorite porphyry dyke clusters and stocks. Vysoká–Zlatno is the largest deposit (13.4 Mt at 0.52% Cu), with mineralised Mg–Ca exo- and endoskarns, developed at the prevolcanic basement level. The alteration pattern includes an internal K- and Na–Ca silicate zone, surrounded by phyllic and argillic zones, laterally grading into a propylitic zone. Fluid inclusions in quartz veinlets in the internal zone contain mostly saline brines with 31–70 wt.% NaCl eq. and temperatures of liquid–vapour homogenization (Th) of 186–575°C, indicating fluid heterogenisation. Garnet contains inclusions of variable salinity with 1–31 wt.% NaCl eq. and Th of 320–360°C. Quartz–chalcopyrite veinlets host mostly low-salinity fluid inclusions with 0–3 wt.% NaCl eq. and Th of 323–364°C. Data from sphalerite from the margin of the system indicate mixing with dilute and cooler fluids. The isotopic composition of fluids in equilibrium with K-alteration and most skarn minerals (both prograde and retrograde) indicates predominantly a magmatic origin (δ¹⁸O_fluid 2.5–12.3‰) with a minor meteoric component. Corresponding low δD_fluid values are probably related to isotopic fractionation during exsolution of the fluid from crystallising magma in an open system. The data suggest the general pattern of a distant source of magmatic fluids that ascended above a zone of hydraulic fracturing below the temperature of ductile–brittle transition. The magma chamber at ∼5–6 km depth exsolved single-phase fluids, whose properties were controlled by changing PT conditions along their fluid paths. During early stages, ascending fluids display liquid–vapour immiscibility, followed by physical separation of both phases. Low-salinity liquid associated with ore veinlets probably represents a single-phase magmatic fluid/magmatic vapour which contracted into liquid upon its ascent.     

Stable isotope study of the mineralization and alteration in the Madjarovo Pb–Zn district,south-east Bulgaria

The Madjarovo ore district is centred on the exposed section of a Lower Oligocene volcano and consists of radially disposed Pb–Zn-precious metal veins and attendant intermediate sulfidation wallrock alteration. Earlier high sulfidation and potassic porphyry style alterations are found in the centre of the district spatially associated with monzonitic intrusions. The total duration of all mineralization and alteration was ca. 300 ka. Stable isotope analyses (S, O, H) have been carried out on a suite of sulfides, sulfates and silicates from the mineralization, high and intermediate sulfidation alterations and a suite of basement rocks. These data range between the following limits: . We also analysed δD of fluid inclusions in quartz and barite for which we obtained, respectively, the ranges of −43.6 to −78.6 and −58.4 to −67.1‰. The data show that high sulfidation alteration was dominated by magmatic fluids with minor meteoric water, whereas the fluids responsible for the intermediate sulfidation alteration were essentially magmatic. The fluids responsible for the intermediate sulfidation Pb–Zn mineralization were mixed magmatic–meteoric and certainly contained a significant meteoric component. Sulphur is likely derived from basement and/or igneous sources. The evolution of alteration and mineralization styles from potassic, porphyry copper style to high sulfidation to intermediate sulfidation can be understood in terms of changing ore fluid composition resulting from an increasing permeability of the system and an increasingly remote source of magmatic fluid with time. These changes link directly to the geological evolution of this volcanic centre.     

The relation between Cu/Au ratio and formation depth of porphyry-style Cu–Au ± Mo deposits

Constraints on gold and copper ore grades in porphyry-style Cu–Au ± Mo deposits are re-examined, with particular emphasis on published fluid pressure and formation depth as indicated by fluid inclusion data and geological reconstruction. Defining an arbitrary subdivision at a molar Cu/Au ratio of 4.0 × 10⁴, copper–gold deposits have a shallower average depth of formation (2.1 km) compared with the average depth of copper–molybdenum deposits (3.7 km), based on assumed lithostatic fluid pressure from microthermometry. The correlation of Cu/Au ratio with depth is primarily influenced by the variations of total Au grade. Despite local mineralogical controls within some ore deposits, the overall Cu/Au ratio of the deposits does not show a significant correlation with the predominant type of Cu–Fe sulfide, i.e., chalcopyrite or bornite. Primary magma source probably contributes to metal endowment on the province scale and in some individual deposits, but does not explain the broad correlation of metal ratios with the pressure of ore formation. By comparison with published experimental and fluid analytical data, the observed correlation of the Cu/Au ratio with fluid pressure can be explained by dominant transport of Cu and Au in a buoyant S-rich vapor, coexisting with minor brine in two-phase magmatic hydrothermal systems. At relatively shallow depth (approximately <3 km), the solubility of both metals decreases rapidly with decreasing density of the ascending vapor plume, forcing both Cu and Au to be coprecipitated. In contrast, magmatic vapor cooling at deeper levels (approximately >3 km) and greater confining pressure is likely to precipitate copper ± molybdenum only, while sulfur-complexed gold remains dissolved in the relatively dense vapor. Upon cooling, this vapor may ultimately contract to a low-salinity epithermal liquid, which can contribute to the formation of epithermal gold deposits several kilometers above the Au-poor porphyry Cu–(Mo) deposit. These findings and interpretations imply that petrographic inspection of fluid inclusion density may be used as an exploration indicator. Low-pressure brine + vapor systems are favorable for coprecipitation of both metals, leading to Au-rich porphyry–copper–gold deposits. Epithermal gold deposits may be associated with such shallow systems, but are likely to derive their ore-forming components from a deeper source, which may include a deeply hidden porphyry–copper ± molybdenum deposit. Exposed high-pressure brine + vapor systems, or stockwork veins containing a single type of intermediate-density inclusions, are more likely to be prospective for porphyry–copper ± molybdenum deposits.     

西南“三江”格咱岛弧斑岩成矿系统

西南“三江”格咱岛弧是“三江”古特提斯演化形成的重要地质构造单元,该单元从晚三叠世洋壳俯冲、洋盆关闭转入碰撞及走滑剪切阶段都产生酸性岩体,形成斑岩Cu-Mo-Au矿床,并构成独立的成矿系统.笔者将格咱岛弧成矿作用以三大岩浆活动期次为基础划分为三套成矿系统,即印支期斑岩Cu多金属成矿系统、燕山期斑岩Mo-Cu多金属成矿系统和喜马拉雅期富碱斑岩Au-Mo-Cu多金属成矿系统.本文从成矿时间、成矿物质来源、成矿流体系统和成矿动力学背景等方面详细总结论述了格咱岛弧的三套斑岩成矿系统.同一地区三大成矿系统反映三次地质构造事件,这种构造演化的连续性和成矿对应性使得该带的研究具有重要意义.     

Variation of Mo isotopes from molybdenite in high-temperature hydrothermal ore deposits

Measurable molybdenum isotope fractionation in molybdenites from different ore deposits through time provides insights into ore genesis and a new technique to identify open-system behavior of Re–Os in molybdenites. Molybdenite samples from six porphyry copper deposits, one epithermal polymetallic vein deposit, four skarns, and three Fe-oxide Cu–Au deposits were analyzed. The δ⁹⁷Mo‰ (where ) for all samples varied from 1.34 ± 0.09‰ to −0.26 ± 0.04‰. This is the largest molybdenum isotopic variation in molybdenite from high-temperature ore deposits recorded to date. δ⁹⁷Mo‰ of molybdenite varies as a function of the deposit type and the rhenium and osmium concentrations of the samples. Isotope values for Mo also vary within the individual deposits. In general, molybdenites from porphyry copper deposits have the lightest values averaging 0.07 ± 0.23‰ (1σ). Molybdenites from the other deposit types average 0.49 ± 0.26‰ (1σ). The variations could be related to the fractionation of Mo into different mineral phases during the ore-forming processes. A comparison of the Mo isotope ratios and the Re–Os ages obtained from the same aliquot may possess a geochronological evaluation tool. Samples that yielded robust ages have different Mo isotopic compositions in comparison to samples that yielded geologically unreasonable ages. Another observed relationship between the Re–Os and Mo isotope data reveals a weak correspondence between Re concentration and Mo isotope composition. Molybdenites with higher concentrations of Re correspond to lighter Mo isotope values.     

A geochemical study of the Sweet Home Mine,Colorado Mineral Belt,USA: hydrothermal fluid evolution above a hypothesized granite cupola

Deposition of quartz–molybdenite–pyrite–topaz–muscovite–fluorite and subsequent hübnerite and sulfide–fluorite–rhodochrosite mineralization at the Sweet Home Mine occurred coeval with the final stage of magmatic activity and ore formation at the nearby world-class Climax molybdenum deposit about 26 to 25 m.y. ago. The mineralization occurred at depths of about 3,000 m and is related to at least two major fluid systems: (1) one dominated by magmatic fluids, and (2) another dominated by meteoric water. The sulfur isotopic composition of pyrite, strontium isotopes and REY distribution in fluorite suggest that the early-stage quartz–molybdenite–pyrite–topaz–muscovite–fluorite mineral assemblage was deposited from magmatic fluids under a fluctuating pressure regime at temperatures of about 400°C as indicated by CO₂-bearing, moderately saline (7.5–12.5 wt.% NaCl equiv.) fluid inclusions. LA-ICPMS analyses of fluid inclusions in quartz demonstrate that fluids from the Sweet Home Mine are enriched in incompatible elements but have considerably lower metal contents than those reported from porphyry–Cu–Au–Mo or Climax-type deposits. The ore-forming fluid exsolved from a highly differentiated magma possibly related to the deep-seated Alma Batholith or distal porphyry stock(s). Sulfide mineralization, marking the periphery of Climax-type porphyry systems, with fluorite and rhodochrosite as gangue minerals was deposited under a hydrostatic pressure regime from low-salinity ± CO₂-bearing fluids with low metal content at temperatures below 400°C. The sulfide mineralization is characterized by mostly negative δ³⁴S values for sphalerite, galena, chalcopyrite, and tetrahedrite, highly variable δ¹⁸O values for rhodochrosite, and low REE contents in fluorite. The Pb isotopic composition of galena as well as the highly variable ⁸⁷Sr/⁸⁶Sr ratios of fluorite, rhodochrosite, and apatite indicates that at least part of the Pb and Sr originated from a much more radiogenic source than Climax-type granites. It is suggested that the sulfide mineralization at the Sweet Home Mine formed from magmatic fluids that mixed with variable amounts of externally derived fluids. The migration of the latter fluids, that were major components during late-stage mineralization at the Sweet Home Mine, was probably driven by a buried magmatic intrusion.     

Sulfur isotopic zonation in the Cadia district,southeastern Australia: exploration significance and implications for the genesis of alkalic porphyry gold–copper deposits

The alkalic porphyry gold–copper deposits of the Cadia district occur in the eastern Lachlan Fold Belt of New South Wales, Australia. The district comprises four porphyry deposits (Ridgeway, Cadia Quarry, Cadia Hill, and Cadia East) and two iron–copper–gold skarn deposits (Big Cadia and Little Cadia). Almost 1,000 tonnes of contained gold and more than four million tonnes of copper have been discovered in these systems, making Cadia the world’s largest known alkalic porphyry district, in terms of contained gold. Porphyry gold–copper ore at Cadia is associated with quartz monzonite intrusive complexes, and is hosted by central stockwork and sheeted quartz–sulfide–(carbonate) vein systems. The Cadia porphyry deposits are characterized by cores of potassic and/or calc–potassic alteration assemblages, and peripheral halos of propylitic alteration, with late-stage phyllic alteration mostly restricted to fault zones. Hematite dusting is an important component of the propylitic alteration assemblage, and has produced a distinctive reddening of feldspar minerals in the volcanic wall rocks around the mineralized centers. Sulfide mineralization is strongly zoned at Ridgeway and Cadia East, with bornite-rich cores surrounded by chalcopyrite-rich halos and peripheral zones of pyrite mineralization. The Cadia Hill and Cadia Quarry deposits have chalcopyrite-rich cores and pyrite-rich halos, and Cadia Hill contains a high-level bornite-rich zone. Distinctive sulfur isotopic zonation patterns have been identified at Ridgeway, Cadia Hill, and Cadia East. The deposit cores are characterized by low δ³⁴S_sulfide values (−10 to −4‰), consistent with sulfide precipitation from an oxidized (sulfate-predominant) magmatic fluid at 450 to 400°C. Pyrite grains that occur in the propylitic alteration halos typically have δ³⁴S_sulfide values near 0‰. There is a gradual increase in δ³⁴S_sulfide values outwards from the deposit cores through the propylitic halos. Water–rock interaction during propylitic alteration caused magmatic sulfate reduction and concomitant oxidation of ferrous iron-bearing minerals, resulting in enrichment of ³⁴S in pyrite and also producing the distinctive reddened, hematite-rich alteration halos to the Cadia deposits. These results show that sulfur isotope analyses have potential applications in the exploration of alkalic porphyry-style deposits, with zones of depleted δ³⁴S_sulfide values most prospective for high-grade mineralization.     

斑岩-浅成低温热液型Cu-Au矿H2O-Cl-S流体性质和演化方式对成矿的制约

斑岩—浅成低温热液型Cu—Au成矿流体最具代表性的是H2O—Cl—S流体。流体的性质强烈控制着Cu、Au的成矿行为,包括溶解性、迁移形式和气—液分配。流体的氧逸度和流体中Cl、S物种相对含量决定金属在流体中的溶解形式,高氧逸度的高温高盐度流体中Cu、Au主要和Cl络合,S-3也可能是促进Au溶解的重要S物种形式。而过量的S有利于Cu、Au等元素以含S离子络合物进入液相流体,与含S中性络合物配分进入气相流体并迁移Au至浅成低温热液环境形成矿床。岩浆需要经历充分的分异,出溶成分和性质有利于金属迁移的流体,形成高品位的斑岩型Cu、Au矿体;上覆叠加浅成低温热液型Au矿体可能需要初始的成矿流体状态进入NaCl—H2O的超临界区、有效的演化方式、良好的流体缓冲环境和有利的Au沉淀场所。相分离和流体—流体反应是沉淀斑岩—浅成低温热液型Cu—Au矿体最重要的流体演化方式。气相流体具有独特的流体性质和演化方式,可能成为十分重要的成矿流体。     

Recycling of orogenic arc crust triggers porphyry Cu mineralization in Kerman Cenozoic arc rocks,southeastern Iran

Pre-collisional Eocene–Oligocene arc diorites, quartzdiorites, granodiorites, and volcanic equivalents in the Kerman arc segment in central Iran lack porphyry Cu mineralization and ore deposits, whereas collisional middle-late Miocene adakite-like porphyritic granodiorites without volcanic equivalents host some of the world’s largest Cu ore deposits. Petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment. Ore-hosting Kuh Panj porphyry intrusions exhibit high Sr (>400 ppm), low Y (<12 ppm) contents, significant REE fractionation (La/Yb > 20), no negative Eu anomalies (Eu/Eu^* ≥ 1), and relatively non-radiogenic Sr isotope signatures (⁸⁷Sr/⁸⁶Sr = 0.7042–0.7047), relative to Eocene–Oligocene granitoids (mainly Sr < 400 ppm; Y > 12; La/Yb < 15; Eu/Eu^* < 1; ⁸⁷Sr/⁸⁶Sr = 0.7053–0.7068). Trace element modeling indicates peridotite melting for the barren Eocene–Oligocene intrusions and a hydrous garnet-bearing amphibolite source for middle-late Miocene ore-hosting intrusions. The presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30–35 to 40–45 km or 12 kbar. The changes in residual mineralogy in the source of Eocene to Miocene rocks in the Kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel. Underplating of Cu and sulfur-rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust–mantle boundary, and dehydration melting under oxidizing conditions produced syn- and post-collisional ore-hosting intrusions, while the lack of post-collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur-rich and oxidized adakitic magmas. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Specific features of the fluid regime during the formation of systems with copper-molybdenum-gold and copper-tin mineralizations (Iskra-Soboliny knot, Kavalerovo ore district, Primorye)

Specific features of the fluid regime in ore-magmatic systems located in the southwestern part of the Kavalerovo ore district (Primorye) are considered. One system is accompanied by mineralization of the porphyry copper type (Lazurnoe deposit); the other system, by tin (copper-tin) mineralization of the hydrothermal type (Iskra deposit). It is shown that the magmatic stages of these systems are distinguished mainly by the chlorophile nature of the copper-gold system and the fluorophile nature of the copper-tin system. The well-known distinction of these systems in terms of the redox parameter is confirmed, and its different evolution scenarios in the systems are shown. The results of the study of fluid inclusions in quartz of postmagmatic associations show that the processes of ore formation at the Lazurnoe deposit were characterized by a wide temperature range and the heterogeneity of the mineral-forming environment. The early period was marked by the coexistence of aqueous-saline brines (mainly of Na-Ca-Mg-chloride composition) and low-density fluid inclusions. The late period was dominated by ordinary hydrothermal solutions. The Iskra deposit formed in a relatively narrow temperature range from homogeneous fluids of essentially Na-chloride composition characterized by moderate and low salinity.     

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