Sebastien Meffre

Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.

Abstract Arsenian pyrite containing above 1 wt. % As plays a crucial role in deposition and deportment of Au and other chalcophile elements. The importance of arsenian pyrite led to theoretical and experimental studies that examined properties and genesis of the mineral; however, the interpretation of the phase relations between arsenian pyrite and arsenopyrite is conflicting. In this contribution, we present the results of a review of the experimental studies that have investigated the crystallisation of pyrite in As-bearing systems, a summary of As content in pyrite coexisting with arsenopyrite in 37 deposits and the composition of arsenian pyrite in deposits with little or no arsenopyrite. The review demonstrates that the previous experimental studies that attempted to achieve an equilibrium between pyrite and arsenopyrite observed about 1 wt. % As or less in pyrite. The literature survey of the assemblages of pyrite and arsenopyrite shows that pyrite crystallising together with arsenopyrite commonly has a very heterogeneous composition with As content varying from below detection to about 10 wt. % As and no clear discontinuities were observed across this range. In the deposits without arsenopyrite, arsenic content in pyrite can reach 20 wt. % As. We consider three principal scenarios of the relations of arsenian pyrite and arsenopyrite: (A) Pyrite with high As content is stable in equilibrium with arsenopyrite. Low-As pyrite coexisting with arsenopyrite is a product of disequilibrium crystallisation; (B) a scenario of control of As content in pyrite coexisting with arsenopyrite by thermodynamic parameters including temperature, pressure, the activity of components and fluid composition and (C) a scenario where arsenian pyrite is a metastable mineral. The experimental and natural observations are inconsistent with a model of 5–6 wt.% As in pyrite coexisting with arsenopyrite in equilibrium (scenario A). The stability range of the assemblage of pyrite and arsenopyrite constrains the thermodynamic control on the composition of pyrite crystallising in equilibrium with arsenopyrite (scenario B). The scenario of metastable crystallisation of arsenian pyrite (C) proposes formation of the mineral by fast growth from oversaturated fluids with As content controlled by surface adsorption and can explain such features as sector zoning of the mineral and the apparent negative temperature dependence of the solubility. The data phase relations of arsenian pyrite highlight the need for new experimental studies, and suggest that the scenario of disequilibrium phase relations of arsenian pyrite should be considered for interpretation of natural assemblages.

Subordinate sapphire accompanies prevalent zircon megacrysts in the Bo Loei basaltic gem field, Ratanakiri Province, Cambodia. These deposits are important for heat-treated gem zircon. Dark blue sapphire, with rare blue-green, orange-brown and yellow stones, up to a few cm in size, include hexagonal-shaped and growth-zoned crystals. Analyses of the sapphires (electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry) showed Fe as the main chromophore (0.6–2.7 wt%), with minor Ti (<0.7 wt%). Sapphire cores show enrichment in Fe relative to rims and some include exotic heavy elements (Nb up to 56, Ta up to 144, Sn up to 5 ppm). The sapphires show high Ga values (271–724 ppm) and Ga/Mg ratios (4.8–77.0) suggesting magmatic associations. Two sapphires with syngenetic inclusions (zircon, Nb-rich rutile) gave U–Pb (Th-disequilibrium corrected) ages at ca 0.93 ± 0.1 Ma. The Bo Loei sapphires show higher Fe and Ga than other magmatic sapphire suites elsewhere in...

The overarching aims of this study are: Determination of gold-containing mineral phases, as well as gold and other trace element contents, in pyrite and arsenopyrite by combining results from Mineral Liberation Analysis (MLA) and laser ablation mass spectrometry (LA-ICPMS) on 10 rock core samples.

809 New insights into the 3.4 Ga sulfur and iron cycle from the ICDP Buck Reef Chert drill core B. EICKMANN1, A. HOFMANN1, A. AGANGI2, M. WILLE3, S. MEFFRE4, B. WING5 AND R. SCHOENBERG3 1Department of Geology, University of Johannesburg, South Africa 2Department of Applied Geology, Curtin University, Australia 3Department of Geosciences, Tübingen University, Germany 4CODES and School of Earth Sciences, University of Tasmania, Australia 5Department of Earth and Planetary Sciences and GEOTOP, McGill University, Canada

12 Magmatic differentiation and/or assimilation and related segregation of immiscible sulfide 13 liquid are generally believed to be critical processes in the formation of the majority of 14 orthomagmatic Ni sulfide deposits. In recent years, a new class of Ni sulfide deposits formed by 15 metasomatic and/or hydrothermal modification of peridotites has been recognized. The 16 serpentinite-hosted Avebury Ni sulfide deposit (Tasmania, Australia), the largest known non17 magmatic deposit, provides an unprecedented opportunity to understand sources of metals and 18 fluids responsible for this style of economic mineralization. Our study shows that 19 serpentinization of the Ni-bearing olivine in the Cambrian peridotites of the McIvor Hill 20 complex was followed by metasomatic transformation assisted by heat and fluids supplied by the 21 nearby Late Devonian granite intrusion. The role of the above in the formation of an economic 22 concentration of Ni sulfides is supported by 1) abundan...

ABSTRACT Malaysia is endowed with a number of major sediment-hosted, orogenic gold deposits that lie parallel to but east of the Bentong-Raub Suture Zone, which runs approximately N-S in central Malaysia. The Selinsing gold deposit is one of the major economic deposits in central Malaysia and is hosted by (meta)-sedimentary units. The deposit is affected by later deformation and metamorphism during the Triassic due to the collision of the Sibumasu Terrane with the Sukhothai Arc. Laser ablation ICP-MS U-Pb zircon dating of the host rocks indicates a Carboniferous (ca. 331-300 Ma) maximum depositional age. Ore minerals include pyrite, arsenopyrite, galena, sphalerite, chalcopyrite, pyrrhotite and gold. Detailed textural and geochemical studies revealed five distinctive pyrite types, sub-rounded framboidal pyrite (Pyrite 1), rounded recrystallized pyrite (Pyrite 2), anhedral inclusion-rich pyrite (Pyrite 3), anhedral to subhedral clean pyrite (Pyrite 4) and coarse euhedral clean pyrite (Pyrite 5). Laser ablation ICP-MS trace element analysis of the framboidal pyrite indicates enrichment in V, As, Mo, Ni, Se, Te, Ag, and Zn relative to the other pyrite types. Pyrite sulfur isotope composition (1.2 – 9.2 ‰) suggests a likely mixture of magmatic and local sedimentary source for the sulfur. Pyrite Pb isotope results (Pb206/Pb204: 18.94-19.10; Pb207/Pb204: 15.72-15.73) suggest a high-U source rock for the lead. Fluid inclusions are CO2-rich (95-100 mole %) and yielded homogenization temperatures from 194 to 348 °C and salinities between 1.23 and 9.98 wt % NaCl equiv. suggesting involvement of metamorphic fluids during ore formation. Based on these results, we suggest a two-stage model for the formation of the gold deposit at Selinsing. Stage 1 consists of early enrichment of the elements Au, V, As, Mo, Se, Te, Ni, Ag, and Zn in framboidal pyrite in the sediments, whereas Stage 2 is characterized by multiple post-diagenetic deformation and metamorphic processes, favouring the development of fluid pathways and Au remobilization into later pyrites. Regionally, the Selinsing gold deposit shares geological similarities (in term of host rocks, ore mineralogy and geochemistry) with many other sediment-hosted, orogenic gold deposits in mainland SE Asia such as the Sepon gold deposit (Laos), Langu gold deposit (Thailand), Modi Taung and Meyon gold deposits (Myanmar), and Phuoc Son gold deposit (central Vietnam). We suggest that our two-stage model may have important implications to mineral exploration for future research on sediment-hosted/orogenic gold deposits in SE Asia.

Mining of larger, lower grade deposits across several commodities (e.g., Cu, Au, Pb, Zn) in recent decades has led to an increase in the quantities of mine wastes being produced. These materials may contain reactive minerals, including sulfides, and therefore require appropriate management to mitigate against environmental impacts including the formation of acid and metalliferous drainage (AMD). Common AMD remediation strategies involve the application of introducing covers and using chemical or biological techniques to stabilise these wastes, though the long-term success of these strategies is not guaranteed as examples across Australia (e.g., Ranger, Mary Kathleen) have demonstrated. Instead, determining if new economy metals or additional base or precious metals are contained in sulfidic mine waste at economic concentrations presents an opportunity to both reduce AMD risk and recover additional commodities. In this study, geometallurgical characterisation of mine tailings at two ...

... arc of the Cordón de Lila (northern Chile) ... A new study of the Cordón de Lila Ordovician volcano-sedimentary successions in northern Chile reveals for the first time an arc assemblage deposited on thin crust within a continental arc system, having regional implica-tions. ...

ABSTRACT Coronation Hill is a U + Au + platinum group elements deposit in the South Alligator Valley (SAV) field in northern Australia, south of the better known unconformity-style U East Alligator Rivers (EAR) field. The SAV field differs from the EAR by having a more complex basin-basement architecture. A volcanically active fault trough (Jawoyn Sub-basin) developed on older basement and then was disrupted by renewed faulting, before being buried beneath regional McArthur Basin sandstones that are also the main hanging wall to the EAR deposits. Primary mineralisation at Coronation Hill formed at 1607 ± 26 Ma (rather than 600-900 Ma as previously thought), and so it is likely that the SAV was part of a single west McArthur Basin dilational event. Most ore is hosted in sub-vertical faults and breccias in the competent volcanic cover sequence. This favoured fluid mixing, acid buffering (forming illite) and oxidation of Fe2+ and reduced C-rich assemblages as important uranium depositional mechanisms. However, reduction of U in fractured older pyrite (Pb model age of 1833 ± 67 Ma) is an important trap in diorite. Some primary ore was remobilised at 675 ± 21 Ma to form coarse uraninite + Ni-Co pyrite networks containing radiogenic Pb. Coronation Hill is polymetallic, and in this respect resembles the `egress'-style U deposits in the Athabascan Basin (Canada). However, these are all cover-hosted. A hypothesis for further testing is that Coronation Hill is also egress-style, with ores formed by fluids rising through basement-hosted fault networks (U reduction by diorite pyrite and carbonaceous shale), and into veins and breccias in the overlying Jawoyn Sub-basin volcano-sedimentary succession.

... Fig. 1. Simplified regional geological map of Bafq Mineral Province (modified after Haghipour, 1977, Soheili and Mahdavi, 1991, Majidi and Babakhani, 1995, [Ramezani and Tucker, 2003], Amini, 2004, Ghaemi and Saidi, 2006 and [Jami et al., 2007]). View thumbnail images. ...

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Earliest Eocene (53 Ma) convergence in the Southwest Pacific; evidence from pre-obduction dikes in the ophiolite of New Caledonia.

A kinematic analysis allows a new interpretation of the metamorphic zoning and tectonic structure of the Upper Eocene high-pressure metamorphic core complex of northern New Caledonia to be proposed. A three-step evolution is proposed: 1) subduction of previously thinned continental crust elements; 2) subduction blocking due to the crustal thickening; 3) crustal thinning and extensional detachment during the diapir-like uplift and unroofing of the eclogitic core. Such a model accounts for the thermobarometric and radiochronologic data, and also for the weakness of substratum deformation and absence of metamorphic sole during the emplacement of the ophiolitic nappe. -English summary

This record presents trace-element and chronologic data collected from zircon and baddeleyite at the Australian Research Council Centre of Excellence in Ore Deposits (CODES) at the University of Tasmania in June 2015. The work was carried out in support of the Northern Territory Geological Survey (NTGS) regional geoscientific investigations and value adds to co- funded drill core acquired during Geophysics and Drilling Collaborations program, Round 2. Isotope data and interpretations for zircon and baddeleyite from samples of Mount Peake Gabbro, Arunta Region in the Northern Territory are presented herein. The Mount Peake Gabbro is a magnetite-rich gabbro and is host to the Mount Peake Fe-V-Ti deposit. The age of the country rocks intruded by the gabbro is unknown but is interpreted to be Palaeoproterozoic thus constraining the maximum crystallisation age of the Mount Peake Gabbro. The samples were collected with the aim of constraining the timing of this episode of mafic magmatism ...

Dispersed gem corundum is mined from placers, commonly from basalt fields, as occurs along eastern Australian and Asian continental margins. New laser ablation inductively coupled plasma mass spectrometry analysis (LA-ICP-MS) of Australian corundum allows genetic distinctions among these suites and gives clues to their primary lithospheric sources prior to basaltic delivery. Bimodal corundum suites at Barrington Tops, Cudgegong-Gulgong-Macquarie River and Yarrowitch, New South Wales (NSW), include lower Ga, higher Mg ‘metamorphic’ and higher Ga, lower Mg ‘magmatic’ groups. The Barrington Tops ‘metamorphic’ corundum is more Fe-rich (av 4500 - 7100 ppm) than Cudgegong- Macquarie River equivalents (av Fe 1800 - 2100 ppm). Yarrowitch corundum is relatively low in Fe, Ti and Cr. Along with other eastern Australian data (north-east Tasmania; New England, NSW) and from gem fields elsewhere, the combined trace element and O isotope data, reveal considerable geographic and genetic variations...

Pyrite and pyrrhotite are commonly associated minerals in many economic deposits and black shales across the world. The metamorphic reduction of diagentic pyrite into pyrrhotite is known to result in the release of sulfur, thereby enabling further formation of other metal- sulfide clusters. We discuss here the various geochemical and and physiochemical transitions that result during this reduction. We observe that diagenetic pyrite has the ability to encorporate a range of trace elements (T.E.), likely sourced from seawater and intertitial pore waters [1] [2], of which, a large majority (e.g. Zn, Cu, Ag, Au and Pb) are liberated during the conversion. We also present preliminary work on a magnetic study of these two sulfide phases where we observe that pyrite has a distinct magnetic characteristic, akin to that of pyrrhotite, at temperatures far below the published phase transition [3] [4]. We present a series of case studies utilising, real-world examples of this transition and com...

Sulfide and oxide trace element geochemical analyses have been conducted on more than 290 drill core samples from 39 drillholes across South Australia, as part of a collaborative project between Centre for Ore Deposit and Exploration Science (CODES), University of Tasmania, and the Geological Survey of South Australia. The project aim was to analyse the mineral chemistry of pyrite, hematite and magnetite across a range of deposit styles in SA, and determine whether the technique could be used to provide insights into, and vector within, the various mineral systems. Pyrite analyses showed discernible trends for individual mineralisation types. For example, pyrite which forms in an IOCG-type environment typically contains Co>>Ni, with varying amounts of As, Te, Ag, and Au. Cobalt, Ni, and As are exclusively lattice-bound, whereas Te, Ag, and Au are commonly hosted as inclusions of Au-Ag telluride phases or electrum (AuAg alloy). Hematite and magnetite analyses from different mag...

The initial stage of Rodinia supercontinent break-up occurred at about 750 Ma. It preceded formation of the Irkutsk and Franklin large igneous provinces (LIPs) at 712 ± 2 to 739 ± 8 Ma. These LIPs were emplaced within the formerly connected Laurentian and Siberian cratons. The Kingash massif is located in the Precambrian Kan terrane in direct contact with the Siberian Craton at its southwestern boundary. It has been linked to an important suite of mafic–ultramafic intrusions that border the southern margin of the Siberian craton, and that have been inferred to belong to the Irkutsk LIP. The massif is also significant, because it hosts platinum group element (PGE)–Cu–Ni-rich mineralization and is the only large deposit in the region. However, despite numerous dating attempts, the age of the massif had not been resolved. A significant difficulty is post-magmatic recrystallization at amphibolite facies that affected the rocks of the massif. In this study we used U–Pb dating of zircon, ...

The post-obduction formations of Grande Terre, New Caledonia, comprise igneous intrusions, regolith cover, and marine and terrestrial sedimentary rocks. Two restricted Late Oligocene granitoid bodies are intruded into the Peridotite Nappe and its substrate in the south of the island. Thick regolith cover developed over the Peridotite Nappe from the Late Oligocene or earlier. The Népoui Group comprises Late Oligocene–Early Miocene mixed marine carbonate and siliciclastic deposits. It mainly reworks the Peridotite Nappe and its regolith cover. Its development pattern is mainly controlled by tectonic uplift and subsidence. The Gwa N'Doro Formation on the eastern coast and the Fluvio-lacustrine Formation in the south are remnants of the Miocene–Present river network. Offshore, thick Oligocene to Neogene sedimentary successions are imaged by seismic surveys on the margins of Grande Terre, although these successions have not been drilled and remain undated. Several dredges have recove...