Ore Deposit Research Research Articles

In situ apatite and carbonate Lu-Hf and molybdenite Re-Os geochronology for ore deposit research: Method validation and example application to Cu-Au mineralisation

The development of laser ablation inductively coupled plasma quadrupole tandem mass spectrometry (LA-ICP-Q-MS/MS) opens new opportunities to rapidly date a variety of hydrothermal minerals. Here we present in situ Lu-Hf and Re-Os dates for hydrothermal apatite and molybdenite, respectively. We further report the first in situ Lu-Hf dates for bastnäsite, dolomite, and siderite, and assess their potential for constraining ore deposit geochronology. For method validation, we report isotope-dilution Lu-Hf dates for apatite reference material Bamble-1 (1102 ± 5 Ma) and calcite reference material ME-1 (1531 ± 7 Ma), enabling improved accuracy on matrix-matched calibration for LA-ICP-MS/MS Lu-Hf dating. The new methods are applied to the Vulcan Iron-Oxide Copper-Gold (IOCG) prospect in the Olympic Cu-Au Province of South Australia. Such deposits have been difficult to accurately date, given the general lack of reliable mineral geochronometers that are cogenetic with IOCG mineralisation. Hydrothermal apatite Lu-Hf dates and molybdenite Re-Os dates demonstrate that mineralisation at Vulcan largely occurred at ca. 1.6 Ga, contemporaneous with the world class Olympic Dam deposit. Our data also indicates that the Lu-Hf system in apatite is more robust than the U-Pb system for determining the timing of primary apatite formation in an IOCG system. We further demonstrate that dolomite can retain Lu-Hf growth ages over an extended time period (>1.5 billion years), providing constraints on the timing of primary ore mineral crystallisation during brecciation and IOCG mineralisation. Finally, late Neoproterozoic (ca. 589–544 Ma) and Carboniferous (ca. 334 ± 7 Ma) Lu-Hf dates were obtained for texturally late Cu-bearing carbonate veins, illustrating that the carbonate Lu-Hf method allows direct dating of Cu remobilisation events. This has important implications for mineral exploration as the remobilised Cu may have been transferred to younger deposits hosted in Neoproterozoic sedimentary basins overlaying the Olympic IOCG province.

Big data mining on trace element geochemistry of sphalerite

The determination of ore genesis is a main challenge in ore deposit research. Advanced and rapid analytical techniques have given rise to the accumulation of massive amounts of geoscientific data. Therefore, it is imperative to conduct data mining on ore geochemical data to efficiently extract useful metallogenic information. In this contribution, 4095 sets of sphalerite trace element data from 86 deposits of different origins (VMS, MVT, porphyry, epithermal, SEDEX, and skarn) were compiled and analyzed. Factor analysis revealed the effects of physicochemical conditions on sphalerite trace element compositions. Specifically, the high Mn-Fe-Cu-Co-In but low As-Ga-Ge-Sb-Pb concentration of sphalerite is commonly related to decreasing pH or increasing temperature; high sulfur fugacity favors the entry of Fe and Co (but not Ga or Sn) into the sphalerite lattice; and high salinity causes enrichment in Cd-Ga-Ge-Mn, but depletion in Ag-Cu-In-Sb. Multivariate statistical analysis reveals that the Mn-Ge-Sn contents in sphalerite have good potential to differentiate among ore genetic types, the Mn-Ge-In are used to determine between magmatic-hydrothermal and non-magmatic-hydrothermal deposits. Furthermore, machine learning models demonstrate high accuracy of sphalerite trace element data in distinguishing ore types, i.e., 93.02 % (random forest) and 92.82 % (gradient boosting), and its reliability was validated by receiver operating characteristics. Additionally, the blind tests by machine learning on sphalerite trace elements indicate that the Qingshuitang deposit (in the Qin-Hang metallogenic belt, South China), have been an MVT deposit, which is also supported by its low-temperature and high-salinity fluids, wallrock alterations (esp. bariteization), and the obvious age distinction between mineralization and local magmatism. This study highlights that machine learning and multivariate statistical analysis on sphalerite trace-element data can differentiate metallogenic origin and conditions.

Multiphase intrusion at the giant Pulang porphyry Cu-Au deposit in western Yunnan (Southwestern China): comparison between ore-causative and barren intrusions

Porphyry Cu-Au deposits (PCDs) have commonly multiphase porphyry intrusions, yet only one (or a few) of the intrusive phase is/are ore-causative. Understanding the criteria to form ore-causative porphyry is important for both ore deposit research and PCD exploration. At the giant Pulang PCD in western Yunnan, there are three generations of porphyries, i.e., (from oldest to youngest) the quartz diorite porphyry (QDP), quartz monzonite porphyry (QMP) and granite porphyry (GP), and only the QMP has major mineralization. Based on ore deposit geology, and zircon U–Pb–Hf–O isotope systematics, we suggested that the QMP is spatially and temporally ore-related. Oxygen fugacity of the QMP and GP magmas is estimated to be higher than that of the QDP. In addition, Hf–O isotope compositions of the QMP and GP are close to those of the average mantle. We suggested that with the continuous Late Triassic subduction of the Garze–Litang ocean basin, the subducted-slab dehydration and the addition of mantle-wedge materials to the ore-forming magmas increased gradually. The younger magmas (e.g., QMP and GP) are thus more oxidized, and have higher water and ore-material contents, giving them higher ore-forming potential. The reason maybe that the late GP is barren may be due to the depletion of ore-forming materials by the main-stage mineralization during the QMP intrusion.

The application of Fe-Cu-Zn isotopes in ore deposit research and prospecting exploration

金属稳定同位素已经广泛应用于矿床学研究以及找矿勘查。金属来源及其成矿过程是金属矿床研究以及找矿勘查中重点关注的基本核心问题。金属稳定同位素这项新技术进一步提高了我们对地壳中金属来源、迁移和富集的认识。这项新技术的优点是我们可以直接从矿石矿物本身获取信息。在本文中，我们重点关注矿石、水、岩石、土壤、植物等测量出的Fe-Cu-Zn同位素分馏，聚焦于Fe-Cu-Zn同位素从最深部岩浆系统开始一直向上延伸到浅部表生系统的过程中Fe-Cu-Zn同位素如何应用于矿床学研究以及找矿勘查，试图展示这些相对较新的技术可以提供的潜在应用范围。经过系统研究和总结，我们认为金属稳定同位素数据可以从三方面加以利用。首先，地表的植物、水、风化的岩石以及土壤中产生的较大的同位素分馏可以作为地下矿产勘查的指示标志；第二，矿区范围内金属稳定同位素往往具有系统的空间变化规律，可以指示成矿热液空间演化模式和矿体延伸方向；第三，金属元素作为成矿元素，其同位素可以直接有效地约束矿石的形成过程、成因以及源区特征。

Ore-forming fluids of the Fancha gold deposit, Lingbao, Henan Province

The Fancha gold deposit is a representative of the auriferous quartz vein type gold deposits in the Xiaoqingling gold district where the ore-forming fluid is one of the key controlling factors in the deposits formation, and also the main focus of ore deposit research. Here, the geological characteristics and fluid inclusions of the Fancha deposit are presented in detail, with a description of the potential origin and evolution of the fluid and the genesis of the deposit. Field investigation and petrographic observation show that ore-bodies in the Fancha deposit are preferentially hosted in the amphibolites of the Taihua Group and are controlled by brittle fracture. Hydrothermal alteration in the Fancha deposit includes silicification, potash feldspathization, sericitization, pyritization and carbonatization. The mineral assemblage, cross-cutting and replacement relationships indicate that the ore-forming process can be divided into quartz-K-feldspar (I), quartz-coarse pyrite (Ⅱ), quartz-fine pyrite (III), quartz-polymetallic sulfide (IV) and carbonate stages (V). Gold is mainly precipitated in stages III and IV. Three types of fluid inclusions have been identified in the Fancha deposit, based on their characteristics at room temperature: three-phase CO2-rich, three-phase CO2-bearing and two-phase aqueous inclusions. The fluid inclusions demonstrate the modes of homogenization temperatures of 363.3℃, 325.5℃, 273℃, 258.62℃ and salinities of 14.53, 9.59, 11.61, 8.03 wt% NaCl.equiv., for stages II, III, IV, and V respectively. The ore-forming fluid in the Fancha deposit belonged to the CO2-H2O-NaCl-(±CH4) fluid system with mid-low temperature and mid-low salinity. The δ18OH2O of the metallogenic fluids was between 1.36 and 6.28, and the δDH2O was between -87 and -53.1. Hydrogen and oxygen isotope data indicate that the ore-forming fluids were dominated by metamorphic fluids in the early stage, and that the metamorphic fluid gradually mixed with circulating meteoric water during the later stages. Petrographic observation and microthermometry suggest that fluid mixing and immiscibility obviously occurred during the main metallogenic stage. Fluid mixing and fluid immiscibility probably led to gold deposition in the Fancha deposit.

Time-resolved, defect-hosted, trace element mobility in deformed Witwatersrand pyrite

The Pb isotopic composition of rocks is widely used to constrain the sources and mobility of melts and hydrothermal fluids in the Earth's crust. In many cases, the Pb isotopic composition appears to represent mixing of multiple Pb reservoirs. However, the nature, scale and mechanisms responsible for isotopic mixing are not well known. Additionally, the trace element composition of sulphide minerals are routinely used in ore deposit research, mineral exploration and environmental studies, though little is known about element mobility in sulphides during metamorphism and deformation. To investigate the mechanisms of trace element mobility in a deformed Witwatersrand pyrite (FeS2), we have combined electron backscatter diffraction (EBSD) and atom probe microscopy (APM). The results indicate that the pyrite microstructural features record widely different Pb isotopic compositions, covering the entire range of previously published sulphide Pb compositions from the Witwatersrand basin. We show that entangled dislocations record enhanced Pb, Sb, Ni, Tl and Cu composition likely due to entrapment and short-circuit diffusion in dislocation cores. These dislocations preserve the Pb isotopic composition of the pyrite at the time of growth (∼3 Ga) and show that dislocation intersections, likely to be common in deforming minerals, limit trace element mobility. In contrast, Pb, As, Ni, Co, Sb and Bi decorate a high-angle grain boundary which formed soon after crystallisation by sub-grain rotation recrystallization. Pb isotopic composition within this boundary indicates the addition of externally-derived Pb and trace elements during greenschist metamorphism at ∼2 Ga. Our results show that discrete Pb reservoirs are nanometric in scale, and illustrate that grain boundaries may remain open systems for trace element mobility over 1 billion years after their formation.

Geochemical characterisation of xenotime formation environments using U-Th

Xenotime (YPO4) is a trace component in many metasedimentary and some igneous rocks, altered rocks and many hydrothermal ore assemblages, where it forms in response to a range of different processes from igneous crystallisation to low-temperature early diagenesis. Due to its wide range of formation temperatures, its suitability and isotopic robustness for reliable U-Pb geochronology, dissolution/precipitation characteristics during overprint events, and widespread occurrence, it is one of the most valuable minerals for U-Pb geochronology leading to four-dimensional (4D) studies of many terranes. The formation environment of xenotime can be deduced from careful petrography and reliable U-Pb in-situ geochronology within a 4D framework. Further, xenotime is a physically robust mineral during sediment transport and may carry distinctive geochemical fingerprints, including age, to secondary environments.From published works, we review the U-Th-contents of well-characterised examples of xenotime formation to provide chemical fingerprints, which assist in identifying the xenotime formation environment. Although the U-Th characteristics of xenotime from all formation environments show considerable overlap, we make the following observations which may be distinctive of some ore formation environments: (i) hydrothermal xenotime formed from low salinity ore fluids (e.g. iron ore and orogenic gold deposits) trend to have the lowest U-contents (<100ppm U) and U/Th (<4), in contrast to xenotime formed from higher salinity ore fluids (Sn-W and base metal deposits); (ii) xenotime associated with unconformity-related U-ores have the highest U-contents at U/Th>10; (iii) diagenetic xenotime has the most variable and highest U/Th, whereas (iv) xenotime from Precambrian orogenic gold deposits has the least variable and lowest U/Th.Petrogenetic inferences from these observations for ore deposit research and exploration include: (i) support for the homogenising effect of the crustal scale of the fluid system in Precambrian orogenic gold deposits, and (ii) the potential for distinctive U-Th geochemical fingerprints for U ores and some Au ores. These characteristics may be reflected in detrital xenotime grains recovered from routine exploration sampling programs.

Preservation and exhumation history of the Harizha-Halongxiuma mining area in the East Kunlun Range, Northeastern Tibetan Plateau, China

The extent to which ore bodies are preserved in orogenic belts remains a poorly understood area of ore deposit research. Using zircon and apatite fission track analysis together with apatite (U-Th)/He dating we constrained the erosion history of the ore bodies in the Harizha–Halongxiuma mining area of the East Kunlun Range, Northern Tibetan Plateau, China. Apatite fission-track ages range from 114±8 to 87±6Ma, with mean track lengths varying from 11.4±1.9 to 12.9±2.0μm. Zircon fission-track ages vary from 205±14 to 142±7Ma. In addition, apatite (U–Th)/He dating yielded ages of 60–56Ma. The thermal history of Jiapigou was modelled based on the apatite fission-track data, including ages and track lengths, with constraints of zircon fission-track ages and (U-Th)/He ages. The exhumation history of the Harizha–Halongxiuma mining area was reconstructed with these age data, revealing that since the early Mesozoic the area has undergone three cooling stages: (1) rapid cooling from 175±30Ma to 100±10Ma with a cooling rate and inferred exhumation of 2.0±0.8°C/Myr and 4.3±1.7km, respectively; (2) a relatively stable stage from 100±10Ma to 40±10Ma with a cooling rate and inferred exhumation of 0.3±0.1°C/Myr and 0.5±0.2km, respectively; and (3) rapid cooling since 40±10Ma with a cooling rate and inferred exhumation of 1.2±0.6°C/Myr and 1.4±0.4km, respectively. This exhumation history is consistent with the subduction process of Pacific plate and the strike slip movements of Dunmi fault. The total exhumation after main mineralization is calculated to be 7.6±3.2km, suggesting that ore bodies in the Harizha–Halongxiuma mining area remain partially preserved.

About this title ‐ Ore Deposits in an Evolving Earth

Ore deposits form by a variety of natural processes that concentrate elements into a volume that can be economically mined. Their type, character and abundance reflect the environment in which they formed and thus they preserve key evidence for the evolution of magmatic and tectonic processes, the state of the atmosphere and hydrosphere, and the evolution of life over geological time. This volume presents 13 papers on topical subjects in ore deposit research viewed in the context of Earth evolution. These diverse, yet interlinked, papers cover topics including: controls on the temporal and spatial distribution of ore deposits; the sources of fluid, gold and other components of orogenic gold deposits; the degree of oxygenation in the Neoproterozoic ocean; bacterial immobilization of gold in the semi-arid near-surface environment; and mineral resources for the future, including issues of resource estimation, sustainability of supply and the criticality of certain elements to society.

Ore deposits in an evolving Earth: an introduction

Abstract Ore deposits form by a variety of natural processes that concentrate elements into a small volume that can be economically mined. Their type, character and abundance reflect the environment in which they formed and thus they preserve key evidence for the evolution of magmatic and tectonic processes, the state of the atmosphere and hydrosphere, and the evolution of life over geological time. This volume presents 13 papers on topical subjects in ore deposit research viewed in the context of Earth evolution. These diverse, yet interlinked, papers cover topics including: controls on the temporal and spatial distribution of ore deposits; the sources of fluid, gold and other components in orogenic gold deposits; the degree of oxygenation in the Neoproterozoic ocean; bacterial immobilization of gold in the semi-arid near-surface environment; and mineral resources for the future, including issues of resource estimation, sustainability of supply and the criticality of certain elements to society.

The Society of Economic Geologists Awards for 2012: R. A. F. Penrose Gold Medal for 2012 * Citation of Robert O. Rye

President Arribas, members, and guests: It is my great privilege to introduce an iconic figure in our field, Robert O. Rye, who is the first Waldemar Lindgren Award winner (1973) and SEG Silver Medalist (1992) to receive the R.A.F. Penrose Gold Medal (2012). In my examination of Bob’s career, three things stand out. First, he is an energetic overachiever with great intellect that made his own luck. Second, he was fortunate to pursue stable isotopes when he entered the field of economic geology in 1963. And last, his integrity, unpretentious style, and friendship enamored all who were lucky enough to work with him. The rest is history. Bob grew up in Los Angeles, where he was a record-setting miler and honor student at Eagle Rock High School. He was Phi Beta Kappa at Occidental College, which got him in the door at Princeton, where he was fortunate to be one of Heinrich Holland’s first graduate students. Dick persuaded him to apply stable isotopes to Providencia, a polymetallic replacement deposit in Mexico, and set him up to perform the analyses in Irving Friedman’s lab at the U.S. Geological Survey in Denver. This pioneering study showed how stable isotopes could be used to understand fluid inputs, histories, and ore-forming processes in an ancient hydrothermal system. This was heady stuff that catapulted Bob to the forefront of ore deposit research. Having proved his ability, he was offered a job at the USGS in 1964. So, he proposed to Fran and they began a new life in Denver. By …

Exploration of the Yandal gold province, Yilgarn Craton, Western Australia

The opening of the Yandal gold province during the 1990s provides a detailed case history of repeated exploration successes. First highlighted in 1992 with the discovery of the Bronzewing gold deposit, the resources of the Yandal gold province grew rapidly through the 1990s with a series of discoveries. By 2000, the gold endowment of the province was 470 tonnes (t), and it was producing 25 t Au p.a. from the Jundee, Bronzewing and Darlot mines. The exploration activities in the deeply weathered and mostly covered Archaean Yandal greenstone belt during this period set the standard for Australian gold exploration in deeply weathered terrains through a twofold approach that involved drilling 100 000 holes, and at the same time making a strong commitment to ore deposit research. Confidence came from an understanding of Archaean gold deposits and the regolith, including the effects of gold dispersion in the weathered zone and the necessity to properly penetrate the Cainozoic cover for effective drill testing. Special emphasis was placed on gold distribution, alteration, lithologies and structural geology, and these soon became the focus of both data collection and drill targeting during the exploration process. Aeromagnetic data provided the platform for interpolation between geologically constrained areas in this province of less than 10% outcrop. Rapid and effective communications and data handling were critical issues for managing large exploration programs involving many geologists in remote areas.

The Society of Economic Geologists 2001 Awards* R.A.F. Penrose Gold Medal for 2001 Citation of Hubert L. Barnes

Mr. President, ladies and gentlemen, my esteemed colleagues, and associates: It is a great honor and privilege to introduce my friend and colleague, and world-class skier, Hubert L. Barnes, this year’s recipient of the Society’s Penrose Gold Medal. The Penrose Gold Medal is the highest honor bestowed on a person for his or her lifetime achievements in and contributions to the field of economic geology. Hu Barnes received a B.S. degree in geology from the Massachusetts Institute of Technology in 1950 and went to work as a mining geologist for the Peru Mining Company in Hanover, New Mexico. After two years, Hu returned to graduate school and received a Ph.D. in economic geology from Columbia University in 1958. He spent four years at the [Carnegie Institution] Geophysical Lab as a postdoctoral fellow doing some of the earliest experimental work on sulfide solubility. He accepted a position as Assistant Professor of Geochemistry at Pennsylvania State University in 1960, and was rapidly promoted to Associate Professor in 1963, and to full Professor in 1966. He was named the Distinguished Professor of Geochemistry in 1990. He was also the Director of the Ore Deposit Research Section for 30 years. Although there is a rumor that he officially retired from Penn State about three years ago, there is very little evidence to support this. He has maintained his hydrothermal laboratory in our department, and comes to the department every day to check if I am taking a nap in my office and to have scientific discussions with his colleagues at lunch time. As President of Applied Research and Exploration, Inc., which sells a unique method of trace level metal determination, …

A Special Issue on Alteration Associated with Volcanic-Hosted Massive Sulfide Deposits, and Its Exploration Significance

This special issue on Alteration Associated with the Spectrum of Volcanic-Hosted Massive Sulfide Deposits and Its Exploration Significance largely reports the results of a three-year (1995–1998) collaborative research project (P439) between the Centre for Ore Deposit Research at the University of Tasmania and the Australian Mineral Industry Research Association (AMIRA). Volcanic-hosted massive sulfide deposits (VHMS) provide a significant contribution to world zinc, copper, lead, silver, and gold production. Some Australian deposits have been very profitably mined because of their particularly high polymetallic grades, high precious metal values, and large size. For example, Rosebery, Que River, and Hellyer were mainstays of the Tasmanian mining industry for several decades. Although VHMS targets have recently gone out of favor—fallen off the radar screens—for many large base metal exploration companies, they continue to be favorable targets for small- to medium-size mining companies. Due to the geological complexity of ancient submarine volcanic terranes, new VHMS deposits are extremely difficult to discover, especially those deposits buried more than a few tens of meters below the surface. The research team at the Centre for Ore Deposit Research and mineral explorers through AMIRA recognized that an improved understanding of alteration zonation was needed to enhance VHMS discovery rates in mature exploration districts. Extensive previous research in submarine volcanic terranes in Australia, North America, Japan, and Europe has documented the mineralogy and geochemistry of various styles of hydrothermal alteration, which are related spatially and genetically to VHMS deposits. Figure 1 illustrates the spatial relationships of seven major alteration styles in VHMS districts, as they were recognized at the beginning of this project. These are summarized below. 1. Footwall alteration pipes exist below most major mound-style VHMS deposits and result from focused upward flow of hydrothermal fluids to the sea floor. Previous studies (e.g., Shirozu, 1974; Riverin and Hodgson, …

Ore deposit research in Germany: a thematic issue dedicated to Professor Günther Friedrich on the occasion of his 70th birthday

Ore deposit research in Germany: a thematic issue dedicated to Professor Günther Friedrich on the occasion of his 70th birthday

The Present Status and future tasks in ore deposit research: U.S.A. and Japan

The Present Status and future tasks in ore deposit research: U.S.A. and Japan