Sequence of mineral formation in clastic ores of the Saf’yanovka volcanic-hosted copper massive sulfide deposit,the Central Urals

The bedded clastic ore widespread on the slopes and flanks of the deeply eroded sulfide mound at the Saf’yanovka volcanic-hosted copper massive sulfide deposit consists of products of destruction of the Paleozoic black smoker along with diverse newly formed sulfides. The size of ore clasts gradually decreases with distance from the massive ore mound, from more than tens of centimeters to a few millimeters. The clastic sediments are characterized by good preservation of sulfide material composed of hydrothermal sedimentary colloform pyrite, chalcopyrite with lamellae of relict isocubanite, and concentrically zoned sphalerite. Numerous pyrite framboids, nodules, and euhedral crystals; chalcopyrite segregations; and twinned sphalerite are typical of sulfide-bearing black shale. Enargite, tennantite, and galena were formed after pyrite, filling interstices between nodules or partially replacing and corroding the previously formed minerals. The interrelations between minerals show that the fine-clastic sulfide-bearing black shale underwent diagenesis in the presence of organic matter.     

Undiscovered Phanerozoic Porphyry Copper Deposits—A Global Assessment

Please refer to the attachment(s) for more details     

The Late Paleozoic porphyry–epithermal spectrum of the Birgilda–Tomino ore cluster in the South Urals,Russia

The Birgilda–Tomino ore cluster in the East Uralian zone, South Urals, Russia, hosts a variety of Late Paleozoic porphyry copper deposits (Birgilda, Tomino, Kalinovskoe, etc.), high- and low sulfidation epithermal deposits (Bereznyakovskoe, Michurino), and skarn-related base metal mineralization (Biksizak) in carbonate rocks. The deposits are related to quartz diorite and andesite porphyry intrusions of the K–Na calc-alkaline series, associated to a subduction-related volcanic arc. We report microprobe analyses of ore minerals (tetrahedrite–tennantite, sphalerite, Bi tellurides and sulfosalts, Au and Ag tellurides), as well as fluid inclusion data and mineral geothermometry. On the basis of these data we propose that the Birgilda–Tomino ore cluster represents a porphyry–epithermal continuum, with a vertical extent of about 2–3 km, controlled by temperature decreases and fS₂ and fTe₂ increase from deeper to shallow levels.     

Geological characteristics and genesis of the Jurassic No. I porphyry Cu–Au deposit in the Xiongcun district,Gangdese porphyry copper belt,Tibet

The Xiongcun district, located in the western segment of the Gangdese porphyry copper belt (GPCB), hosts the only known Jurassic mineralization in the GPCB, Tibet, PRC. The No. I deposit in the Xiongcun district is related to the Middle Jurassic quartz diorite porphyry (167–161 Ma) and the mineralization was formed at ca. 161.5 ± 2.7 Ma. Ore-bearing Middle Jurassic quartz diorite porphyry emplaced into the Early Jurassic volcano-sedimentary rock sequences of the Xiongcun Formation. Veinlets and disseminated mineralization developed within the Middle Jurassic quartz diorite porphyry and the surrounding metamorphosed tuff, hosting a measured and indicated resource of 1.04 Mt copper, 143.31 t gold and 900.43 t silver with an average grade of 0.48% copper, 0.66 g/t gold, and 4.19 g/t silver. The mineralization can be assigned to four stages, including three main stages of hypogene mineralization and one epigenetic stage. The main alteration associated with mineralization is potassic. Seven mineralization-related hydrothermal veins have been recognized, including quartz–sulfide, biotite–sulfide, magnetite–sulfide, quartz–molybdenite–sulfide, chalcopyrite–pyrite–pyrrhotite, pyrite and polymetallic veins. The S and Pb isotopic compositions of the ore sulfides and the Re contents of the molybdenite suggest a mantle source for the ore-forming materials with minor contamination from the subducted sediments. Hydrogen and oxygen isotope compositions of quartz in the ores suggest that both magmatic and meteoric waters were involved in the ore-forming process. The ore-bearing porphyry (167–161 Ma) and ore-forming (161.5 ± 2.7 Ma) ages of the No. I deposit correspond to the time of northward subduction of Neo-Tethys oceanic slab. The geochemical data of the ore-bearing porphyry indicate that the No. I deposit formed in an intra-oceanic island arc setting and the ore-bearing porphyry originated from the partial melting of mantle with limited contribution of subducted sediments. The genesis of the ore-bearing porphyry and No. I deposit is interpreted as being related to northward intra-oceanic subduction of Neo-Tethys oceanic slab in the Middle Jurassic time (167–161 Ma).     

Geochemical element mobility during alteration/mineralization in the Sungun porphyry copper deposit,Azerbaijan–Iran

The Sungun porphyry copper deposit of northwestern Iran is associated with Miocene diorite/granodiorite to quartz-monzonite intrusive into Eocene volcanic–sedimentary and Cretaceous carbonate rocks. Three main mineralization-related alteration episodes (I, potassic; II, transition; and III, phyllic alterations) were studied in terms of mass transfer during hydrothermal evolution of the Sungun deposit. Isocon plots (Grant, J.A. 1986 Grant, J.A. 1986. The isocon diagram – a simple solution to Gresens’ equation for metasomatic alteration. Economic Geology, 81: 1976–1982. [Crossref], [Web of Science ®] , [Google Scholar], The isocon diagram – a simple solution to Gresens’ equation for metasomatic alteration: Economic Geology, v. 81, p. 1976–1982) were employed to illustrate these changes quantitatively. These plots illustrate that Al, Ti, and Ga were relatively immobile during alteration, and that the alteration was essentially mass-conservative. At all stages in the evolution of the hydrothermal system, computed volume changes were close to zero. In the potassic alteration zone, an obvious enrichment of K and depletions of Na, Ca, Mn, and Fe took place. These changes were due to replacement of plagioclase and amphibole by K-feldspar and biotite, respectively. Potassic alteration was associated with significant addition of Cu, as might be expected from the occurrence of disseminated chalcopyrite and bornite in this zone. In the transition alteration zone, Ca was added, Na, Fe, and Mg were relatively unchanged, and K, Ba, and Cu were depleted. The loss of K and Ba relative to Na reflects replacement of K-feldspar by albite. Phyllic alteration was accompanied by the depletion of Na, K, Fe, and Ba and enrichment of Si and Cu. The losses of Na, K, and Fe reflect the sericitization of alkali feldspar and destruction of ferromagnesian minerals. The addition of Si is consistent with the widespread silicification, which is a major feature of phyllic alteration and the addition of Cu with mobilization from the transition zone, which is depleted in this element.     

Advances in research of the time scales of porphyry deposits: A case study of the Yulong porphyry Cu-Mo deposit in the eastern TibetSCIEI北大核心CSCD

精确限定多期次岩浆-热液活动的时间尺度一直是剖析斑岩矿床形成过程的热点和难点。借助矿物的高精度同位素定年、热力学数值模拟以及石英的钛扩散模型等方法,斑岩矿床中岩浆-热液活动的时间尺度已经被限定在几万年之内。本文以三江特提斯超大型玉龙斑岩铜(钼)矿床为例,重点识别含矿热液脉中普遍存在的石英,利用钛元素的扩散年代学方法,精确限定斑岩矿床中多期岩浆-热液流体活动的时间尺度。扩散模型表明玉龙斑岩矿床热液活动的时间尺度为32000~870000年,有力支持了超大型斑岩矿床可以在几万至几十万年甚至更短时间内形成的观点。此外,为避免钛扩散模型产生较大的误差,需要在精确测定石英中钛含量的基础上,结合矿床地质背景或其他实验方法合理地估测温度和压力条件。研究认为,将矿物的高精度同位素定年与元素的扩散年代学相结合,可以在更为精细的尺度上完善斑岩矿床岩浆-热液活动的时间框架。     

Trace elements in pyrite from the Petropavlovsk gold–porphyry deposit (Polar Urals): Results of LA-ICP-MS analysis

The first study of the pyrite composition from gold deposit in the Urals by the LA-ICP-MS method has been carried out. In the pyrite high contents of Au (up to 49 ppm), Ag (105 ppm), and other micronutrients (As (417 ppm), Ag (105 ppm), Co (2825 ppm), Ni (75 ppm), Cu (1442 ppm), and Zn (19 ppm)) were detected. Furthermore, an increase in the concentrations of trace elements from early to later generations of pyrite (from Py-1 to Py-3) Au, Ag, Te, Sn, Te, and Bi and depletion of Co, As, and Ni have been revealed. Gold is mainly concentrated in the pyrite of the second generation (Py-2) and occurs mostly as an “invisible” form with prevalence of nano-sized particles of native Au, similar in composition to electrum AuAg, as well as Au- and Au–Ag tellurides. The presence in the pyrite of admixtures of Cu, Co, Ni, Pb, As, and Te, possibly favors the entrance of Au into it (up to 5–50 ppm), while in common pyrite, poor in the mentioned impurities, the gold content is <1 ppm.     

First find of platinum group metals in the ore of Kirganik copper–porphyry deposit (Kamchatka)

The Kirganik copper–porphyry deposit is situated in the central part of the Sredinnyi Mountain Range of Kamchatka and is confined to fields of development of potassic orthoclase metasomatite and hypabyssal intrusions of shonkinite. Platinum group metals (PGMs), such as merenskyite, kotulskite, keithconnite, and temagamite, were discovered in the chalcopyrite–bornite and chalcopyrite–bornite–chalcosine ore of the deposit for the first time.     

Geochemical contamination in the mine affected soil of Raniganj Coalfield——A river basin scale assessment

The study aimed to assess the heavy metals(K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Pb, Sr, Zr) contamination in the soil of mine affected Singaran river basin and to analyse spatial variation in the contamination level considering 32 soil samples. Elemental analysis of soil samples has been performed through Energy Dispersive X-ray Analysis(EDX) to quantify the elemental concentration(mg kgà1). Heavy metal concentrations have been assessed through geo-accumulation index(Igeo) and enrichment factor(EF).Indices showed soils have moderate accumulation of most of the metals with moderate enrichment of Sr,Zr, Zn, Cu and Ni. Soil contamination level assessment has been carried out using indices like Contamination Factor(CF), degree of contamination(C_(deg)), modified degree of contamination(m C_(deg)) and Pollution Load Index(PLI). CF shows moderate to considerable contamination by Sr, Zr, Ca, Cu, Mn, Zn and Ni. Mean indices values(m C_(deg)and PLI for the entire basin are 3.38 and 2.23 respectively) show low to moderate level of soil contamination. These indices result have been mapped and analysed in GIS platform to get spatial variation of pollution level. Opencast mines dominate middle catchment area and so is comparatively contaminated. Sample sites 11, 18 and 25 evidenced high values of all indices of pollution load. From the ecological standpoint Ecological Risk Factor(Er) and Potential Ecological Risk Index(RI) have been estimated to assess regional threat to native soil environment and it shows low ecological risk potential. Analysis shows that mine dominated soil of the entire Singaran basin is less contaminated in all respect but tends to the moderate contamination level at the mid-catchment area,especially by Sr, Zr, Zn, Cu and Ni.     

Trace element composition of near-surface silica deposits—A powerful tool for detecting hydrothermal mineral and energy resources

Extensive Paleozoic sinter deposits occur at the surface associated with sub-surface quartz veining and epithermal Au mineralisation in the Drummond Basin, Australia. We investigated the trace element composition of the sinter deposits and quartz veins in an attempt to develop a new geochemical exploration guide for geological resources. The Drummond Basin hydrothermal silica deposits are unique in having anomalously enriched incompatible element (Cs, Li, Be, U, Th and REE) concentrations in comparison to hydrothermal quartz veins from various granitic-pegmatitic systems elsewhere. The development of relative Ce deficiencies (Ce/Ce*_norm < 1) in silica deposits indicate preferential mobilisation of REE over Ce from source rocks by oxidised hydrothermal fluids, leading to relative Ce enrichment in the source material (e.g., rhyolite intrusions). Sinters and quartz veins and some volcanic source rocks show a conspicuous positive Y anomaly relative to REE. This is interpreted in terms of Y fractionation due to fluorine complexation with REE during hydrothermal activity. The majority of sinter and quartz samples within or near the Au mineralisation zone are more enriched in mobile elements (Cs, Li, Rb and Be) than the silica deposits from areas distal to the mineralised area. Normalised Y–REE patterns of the sinter deposits, quartz veins, and wall rocks provide important information on the physico-chemical environment of epithermal mineral deposition in geothermal systems. Trace element systematics as revealed in the current study, particularly in relation to the alkali element mobility, have significant implications for finding new prospect areas and evaluating the potential of existing prospect areas for epithermal metal deposits and active geothermal fields.     

Geology of the Jiama porphyry copper–polymetallic system,Lhasa Region,China

The Jiama deposit, located in the eastern part of the well-known Gangdese Metallogenic Belt on the Tibetan Plateau, is the largest porphyry Cu–polymetallic system in the region, with the largest exploration budget, and is economically viable in the Gangdese Belt to undergo large-scale development. The deposit is well preserved and has experienced little erosion. The proven resources of the deposit are 7.4 Mt Cu, 0.6 Mt Mo, 1.8 Mt Pb + Zn, 6.65 Moz Au, and 360.32 Moz Ag. The results presented in this paper are based on geological and tectonic mapping, geological logging, and other exploration work performed by members of the Jiama Exploration Project Team over a period of 6 years. We propose that the Jiama porphyry Cu–polymetallic system is composed of skarn Cu–polymetallic, hornfels Cu–Mo, porphyry Mo ± Cu, and distal Au mineralization. The development of skarn Cu–polymetallic orebodies at the Jiama deposit was controlled mainly by the contact zone between porphyries and marbles, an interlayer detachment zone, and the front zone of a gliding nappe structure. The hornfels Cu–Mo and porphyry Mo ± Cu orebodies were controlled mainly by a fracture system related to intrusions, and the distal Au mineralization resulted from late-stage hydrothermal alteration.On the basis of field geological logging, optical microscopy, and chemical analysis, we verify that the alteration zones in the Jiama deposit include potassic, phyllic, propylitic, and argillic alteration, with a local lithocap, as well as endoskarn and exoskarn zones. The endoskarn occurs mainly as epidote alteration in quartz diorite porphyry and granite porphyry, and is cut by massive andradite veins. The exoskarn includes garnet–pyroxene and wollastonite skarn, in which the mineralogy and mineral chemical compositions display an outward zonation with respect to the source porphyry. From the proximal skarn to the intermediate skarn to the distal skarn, the garnet/pyroxene ratio varies from > 20:1 to ~ 10:1 to ~ 5:1, the garnet color varies from red-brown to brown-green to green-yellow, and the average composition of garnet varies from Ad_80.1Gr_18.9(Sp + Py)_1.0 to Ad_76.3Gr₂₃(Sp + Py)_0.7 to Ad_59.5Gr_39.5(Sp + Py)_1.0, respectively. The pyroxene is not as variable in composition as the garnet, and is primarily light green to white diopside with a maximum hedenbergite content of ~ 20% and an average composition of Di_88.6Hd_8.9Jo_2.5. From the proximal skarn to the intermediate skarn to the distal skarn, the mineralization changes from Cu–Mo to Cu ± Mo to Pb–Zn ± Cu ± Au ores, respectively. The wollastonite skarn displays no zonation and hosts mainly bornite mineralization. The Cu and Mo mineralization is closely related to the potassic and phyllic zones in the porphyry–hornfels.Zircons from four mineralized porphyries yield U–Pb ages of 15.96 ± 0.5 Ma, 15.72 ± 0.14 Ma, 15.59 ± 0.09 Ma, and 15.48 ± 0.08 Ma. The Re–Os ages of molybdenite from the skarn, hornfels, and porphyry are 15.37 ± 0.15 Ma, 14.67 ± 0.37 Ma, and 14.66 ± 0.27 Ma, respectively. The present results are consistent with the findings of previous research on fluid inclusions, isotopes, and other such aspects. On the basis of the combined evidence, we propose a porphyry Cu–polymetallic system model for the Jiama deposit and suggest a regional exploration strategy that can be applied to prospecting for porphyry-skarn mineralization in the Lhasa area.     

A probabilistic model for rainfall—induced shallow landslide prediction at the regional scale

This paper presents a new probabilistic physically-based computational model (called PG_TRIGRS) for the probabilistic analysis of rainfall-induced landslide hazard at a regional scale. The model is based on the deterministic approach implemented in the original TRIGRS code, developed by Baum et al. (USGS Open File Report 02–424, 2002) and Baum et al. (USGS Open File Report 08–1159, 2008). Its key innovative features are: (a) the application of Ordinary Kriging for the estimation of the spatial distributions of the first two statistical moments of the probability density functions of the relevant soil properties over the entire area, based on limited available information gathered from available information from limited site investigation campaigns, and (b) the use of Rosenblueth’s Point Estimate method as a more efficient alternative to the classical Monte Carlo method for the reliability analysis performed at the single-cell level to obtain the probability of failure associated to a given rainfall event. The application of the PG_TRIGRS code to a selected study area located in the Umbria Region for different idealized but realistic rainfall scenarios has demonstrated the computational efficiency and the accuracy of the proposed methodology, assessed by comparing predicted landslide densities with available field observations reported by the IFFI project. In particular, while the model might fail to identify all individual landslide events, its predictions are remarkably good in identifying the areas of higher landslide density.     

New thermochronologic constraints on the evolution of the Zaldívar porphyry copper deposit,Northern Chile

Life spans and thermal evolution of hydrothermal systems are of fundamental metallogenic importance. We were able to establish the chronology and cooling history of the Zaldívar porphyry copper deposit (Northern Chile) by applying a combination of different isotopic dating methods in minerals with different closure temperatures, including ⁴⁰Ar/³⁹Ar geochronology and zircon fission track thermochronology, together with fluid inclusion thermometry and previous published U–Pb zircon geochronology. The hydrothermal mineralization in the Zaldívar deposit is genetically related to the Llamo Porphyry unit. Samples of igneous biotites from this intrusion yielded ⁴⁰Ar/³⁹Ar plateau ages between 35.5 ± 0.7 and 37.7 ± 0.4 Ma defining a weighted average of 36.6 ± 0.5 Ma (2σ). In contrast, one sample from the Zaldívar porphyry, one from the andesites, and two from the Llamo porphyry yielded considerably younger fission track ages of approximately 29 Ma with a weighted mean for all ages of 29.1 ± 1.7 Ma (2σ). Thermal and compositional constraints for the hydrothermal system in the Zaldívar deposit from fluid inclusions thermometry show that at least three fluid types broadly characterize two main hydrothermal episodes during the evolution of the deposit. The main mineralization and alteration event is characterized by high temperature (above 320°C) hypersaline fluids (salinity between 30 and 56 wt.% NaCl equivalents) coexisting with low-density gas-rich inclusions (salinity less than 17 wt.% NaCl equivalents) that homogenizing into the gas phase at temperatures above 350°C. The second episode corresponds to a low-temperature event which is characterized by liquid-rich fluid inclusions that homogenize into the liquid phase at temperatures ranging from 200°C to 300°C with salinities lower than 10 wt.% NaCl equivalents. The ⁴⁰Ar/³⁹Ar data (36.6 ± 0.5 Ma, weighted average) obtained from igneous biotites represent the minimum age for the last high-temperature (above 300°C) hydrothermal pulse. When compared with previously published U–Pb ages (38.7 ± 1.3 Ma) in zircons from the Llamo porphyry, a close temporal relationship between crystallization of the parental intrusion and the thermal collapse of the last high-temperature hydrothermal event is evident. Cooling took place from approximately 800°C (crystallization of the intrusive complex defined by zircon U–Pb ages) to below 300 ± 50°C (biotite ⁴⁰Ar/³⁹Ar closure temperature) within approximately 1.5 m.y. Because the thermal annealing of fission tracks in zircons occurs at temperatures of 240 ± 30°, the zircon fission track (ZFT) ages of 29.1 ± 1.7 Ma (2σ) mark the end of the thermal activity in the Zaldívar area, specifically the time when the whole area cooled below this temperature, well after the collapse of the main hydrothermal event in the Zaldívar porphyry copper deposit. This cooling age roughly coincides with the age defined for the emplacement of dacitic dikes at 31 ± 2.8 Ma (2σ) (published K–Ar whole rock), 5 km south of the Zaldívar deposit, in the Escondida area. This late magmatic pulse probably is responsible for high heat flow in the Zaldívar deposit as late as 29 Ma. There is no evidence that the low temperature hydrothermal pulse recognized by fluid inclusion studies is related to this thermal event. The zircon fission track cooling ages are interpreted to be related to the time lag required for complete relaxation of the perturbation of the isotherms in the geothermal field imposed by the intrusion of magmatic bodies, with or without any association with low temperature hydrothermal activity.     

Discussion on exploitation of mineral resources and ecological environmental issues in Wenquan, Wushan

Through elementary geophysical prospecting, chemical exploration and geological exploration, there are above 100000 t Mo reserves in Wenquan Wushan, Northwest China. Presently, the molybdenum mine has gone deploitation and construction. Data from drillings indicated many associated elements such as Cu, Pb, Zn, etc. with Mo. Through complete water quality analysis, we found water here comes up to drinking-water standard. This paper investigated the environmental geochemistry characteristics and evaluated water quality in mine field under existing conditions, which may present reference for forecasting the trends of environmental pollution change, underwater environmental monitoring and protection after exploitation. In exploitation of mineral areas, the surroundings of ore areas and groundwater environmental quality are affected correspondingly. The paper analyzed benefication process and tailing disposal process, and consequently, predicted pollution sources, pollution pathway and post-effect that may come along. Also, the interactions between water and rocks with human activity are discussed.     

Magnetic polarity zonation within the El Teniente copper–molybdenum porphyry deposit, central Chile

El Teniente porphyry copper deposit, the world’s greatest intrusion-related Cu–Mo ore body, is hosted within basaltic–andesitic volcanic and gabbroic rocks (mafic complex). This ore body is strongly affected by multiple events of alteration/mineralization with pervasive potassic and chloritic alteration and coetaneous with associated copper mineralization. We present paleomagnetic results obtained from oriented samples at four locations within the mine and from two drill cores, 200 and 400 m long, respectively. Samples are representative of all the main hydrothermally altered rock units, with emphasis on the mafic host rock and dacitic (Teniente dacite porphyry) and dioritic porphyry intrusions. Magnetic experiments [hysteresis loop, isothermal remanent magnetization (IRM), k–T curves, thermal, and alternating field demagnetization] show the presence of prevailing magnetite. Microscope and SEM observations show two families of magnetite, (a) large multidomain magnetite grains, associated with biotite and chlorite of various different hydrothermal alteration events, and (b) abundant small to medium grain-size magnetite (<10 μm) contained within plagioclase, either related to an early Na–Ca–Fe alteration or included within plagioclase during magmatic crystal growth. While the Teniente dacite porphyry and the quartz diorite–tonalite have low magnetic susceptibility (<0.0005 SI) and low natural remanent magnetization (NRM, 10⁻⁴–10⁻³ Am⁻¹), the mineralized mafic host rocks have usually high susceptibility (>0.01 and up to 0.2 SI) with NRM in the range 0.1–2 Am⁻¹. Most mafic complex rock samples have univectorial magnetizations during alternating field or thermal demagnetization. Within the mine, the magnetic polarity is spatially distributed. In the northern part of the deposit, the Teniente dacite porphyry, the associated hydrothermal breccias, and the hosting mafic complex record a reverse polarity magnetization, also observed in the El Teniente sub-6 mine sector immediately to the east and southeast. In the eastern part of the deposit, a normal polarity is observed for samples of the mafic complex from the two long drill cores. There is no evidence for superimposed magnetizations of opposite polarities in samples of the mafic complex. Anhysteretic remanent magnetization (ARM) in a DC field of 40 μT and NRM have similar magnitude and comparable behavior upon alternating field demagnetization. The well-defined strong remanent magnetizations associated with high unblocking temperatures (>500°C) indicate an acquisition of remanent magnetization during mineralization by circulating high temperature fluids related with ore deposition. Paleomagnetic results and the recorded polarity zonation suggest multiple mineralization events occurred at El Teniente, each one with its own evolution stages, superimposed within the district. These results indicate that a simplified broad four-stage model for El Teniente, as presented and overly employed by many authors, divided in (1) late magmatic, (2) main hydrothermal, (3) late hydrothermal, and (4) posthumous stage, does not recognize various short-lived single mineralization events, some superimposed and some distinctly separated in time and space. There is no paleomagnetic evidence for post-mineralization deformation     

Alteration and mineral zonation at the Mt Lyell copper–gold deposit,Tasmania

The Mount Lyell copper deposits are located in the middle Cambrian Mount Read volcanic belt of western Tasmania and consist of more than 24 separate copper–gold–silver orebodies. The dominant copper mineralisation style is disseminated pyrite–chalcopyrite subvertical pipes with subordinate chalcopyrite–bornite ± other copper phases, massive pyrite and base metal sulfides. A zonation in mineralisation style within the pipes is defined from chalcopyrite–magnetite at depth to chalcopyrite–pyrite at intermediate levels, to chalcopyrite–bornite at the shallowest level. Alteration is developed broadly symmetrically around the ore zones and zoned from quartz–chlorite–phengite ± biotite at depth to quartz–muscovite at intermediate levels, and a quartz–muscovite–pyrophyllite–zunyite assemblage at the shallowest levels. This is interpreted to be a result of a fluid that evolved from hot, reduced and neutral conditions at depth to cool, oxidised and acidic conditions at the shallowest level. The chalcopyrite–bornite deposits occur at the top of the hydrothermal system and are associated with intensely silicified rock and muscovite/pyrophyllite alteration. The close relationship of these deposits with the top of the pipes suggests they are part of a single mineralising event. Where the chalcopyrite–bornite deposits are juxtaposed with the Owen Group, rather than a simple chalcopyrite–bornite mineralogy, there are numerous other copper phases, which represent higher oxidation states and collectively suggest variable and fluctuating fluid conditions during deposition. It is proposed that these deposits are formed by an interaction of the reduced hydrothermal fluid with an oxidised fluid generated at very shallow levels within and during deposition of the Owen Group. Mineralisation within the middle Owen Group sandstones and clasts of altered rock within the middle and upper Owen Group sediments marks the end of the hydrothermal system. Around the entire edge of the Mt Lyell field, there is a variation in the white mica composition from proximal muscovite to distal phengite that represents the neutralisation of the hydrothermal fluid by fluid–wall rock interaction.