Applying the box plot to the recognition of footwall alteration zones related to VMS deposits in a high-grade metamorphic terrain, South Africa, a lithogeochemical exploration application

Theart, H.F.J.; Ghavami-Riabi, R.; Mouri, Hassina; Gräser, Peter

doi:10.1016/j.chemer.2010.09.002

Cited by 15 publications

(8 citation statements)

References 14 publications

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“…Gahnite-corundum intergrowth is observed in the finer size fractions of the down ice till samples. Corundum has been previously noted in association with gahnite at the Geco VMS deposit, Canada, by Spry [57] and is considered part of a mineral assemblage formed following high-grade metamorphism of chloritic precursor rocks [58]. These chloritic precursor rocks are characteristic of the footwall hydrothermal alteration pipes of VMS deposits [15].…”

Section: Corundummentioning

confidence: 99%

Exploration Potential of Fine-Fraction Heavy Mineral Concentrates from Till Using Automated Mineralogy: A Case Study from the Izok Lake Cu–Zn–Pb–Ag VMS Deposit, Nunavut, Canada

et al. 2020

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Exploration under thick glacial sediment cover is an important facet of modern mineral exploration in Canada and northern Europe. Till heavy mineral concentrate (HMC) indicator mineral methods are well established in exploration for diamonds, gold, and base metals in glaciated terrain. Traditional methods rely on visual examination of >250 µm HMC material, however this study applies modern automated mineralogical methods (mineral liberation analysis (MLA)) to investigate the finer (<250 µm) fraction of till HMC. Automated mineralogy of finer material allows for rapid collection of precise compositional and morphological data from a large number (10,000–100,000) of heavy mineral grains in a single sample. The Izok Lake volcanogenic massive sulfide (VMS) deposit, one of the largest undeveloped Zn–Cu resources in North America, has a well-documented fan-shaped indicator mineral dispersal train and was used as a test site for this study. Axinite, a VMS indicator mineral difficult to identify optically in HMC, is identified in till samples up to 8 km down ice. Epidote and Fe-oxide minerals are identified, with concentrations peaking proximal to mineralization. Corundum and gahnite are intergrown in till samples immediately down ice of mineralization. Till samples also contain chalcopyrite and galena up to 8 km down ice of mineralization, an increase from 1.3 km for sulfide minerals in till previously reported for coarse HMC fractions. Some of these sulfide grains occur as inclusions within chemically and physically robust mineral grains and would not be identified visually in the coarse HMC visual counts. Best practices for epoxy mineral grain mounting and abundance reporting are presented along with the automated mineralogy of till samples down ice of the deposit.

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Section: Corundummentioning

confidence: 99%

Exploration Potential of Fine-Fraction Heavy Mineral Concentrates from Till Using Automated Mineralogy: A Case Study from the Izok Lake Cu–Zn–Pb–Ag VMS Deposit, Nunavut, Canada

et al. 2020

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“…7; Large et al, 2001). The alteration box plot has also been applied successfully to metamorphosed VMS deposits (Theart et al, 2010). The alteration indices used in this diagram do not consider mass changes of Si in the hydrothermal system.…”

Section: Characterization Of Hydrothermal Alteration and Identificatimentioning

confidence: 99%

Systematics of Hydrothermal Alteration at the Falun Base Metal Sulfide Deposit and Implications for Ore Genesis and Exploration, Bergslagen Ore District, Fennoscandian Shield, Sweden

Kampmann

Jansson

Stephens

et al. 2017

EconGeo

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The Paleoproterozoic Falun Zn-Pb-Cu-(Au-Ag) pyritic sulfide deposit in the Bergslagen ore district, Sweden, is enveloped by hydrothermally altered rocks metamorphosed to the lower amphibolite facies. Immobile-element ratios suggest that the alteration precursors were volcanic rocks of mainly rhyolitic to dacitic composition. Least altered examples of these rocks plot along magmatic fractionation trends outlined by late-to post-ore feldsparphyric metadacite dikes and post-ore granitoid plutons, consistent with a comagmatic relationship between these calc-alkaline, coeval (<10-m.y.) suites. Dolomite or calcite marble, as well as diopside-hedenbergite or tremolite skarn, form subordinate but important lithologic components in the hydrothermally altered zone. Marble occurs as fragments in the massive pyritic sulfide mineralization, suggesting that at least some mineralization formed by carbonate replacement. Mass-change calculations suggest that the hydrothermally altered volcanic rocks gained Mg and Fe and generally lost Ca, K, and Na. Proximal, quartz-anthophyllite-rich altered rocks additionally gained Si, whereas several types of biotite-rich altered rocks lost this element. These mass changes along with mineral chemical data for anthophyllite, biotite, cordierite, and garnet, and the common occurrence of quartz indicate that chloritization, sericitization, and silicification were the dominant premetamorphic alteration styles. A zonation from distal sericitized and silicified volcanic rocks to intermediate sericitized rocks, partly overprinted by chloritization (Mg-rich chlorite), and proximal siliceous and intensely chloritized (Fe-rich chlorite) rocks has been identified. Furthermore, mass changes in more peripheral parts of the altered zone toward the southeast of the deposit suggest that the alteration weakens gradationally toward the volcanic and subvolcanic rocks surrounding the deposit. These patterns represent vectors toward mineralization. Intensely chloritized rocks, largely represented by a single, rhyolitic precursor, envelop the central pyritic massive sulfide bodies to the east, south, and west, supporting a structural model in which the massive sulfide mineralization formed the stratigraphically highest preserved unit in the center, surrounded in a tubular manner by stratigraphic footwall rocks. The northern side represents a portion of the footwall, which was separated by a major shear zone. These spatial relationships also have implications for near-mine exploration, since quartz-rich footwall rocks locally host disseminated to semimassive stockwork Cu-Au mineralization. Cooling of a hot (300°-400°C), acidic (pH ≤4) and reducing fluid carrying metals and sulfur is suggested for formation of stockwork Cu-Au vein mineralization and hydrothermal alteration in the stratigraphic footwall. The Zn-Pb-Cu-rich massive sulfide mineralization is inferred to have formed by fluid neutralization upon interaction with carbonates and mixing with cooler seawater upon fluid entry into porous pumice breccia in a su...

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“…However, the deformed orebodies exhibit textural features, such as mylonitic, cataclastic and press-solution textures, replacing rim and durchbewegung textures, make them deviate from the primary ones and illustrate that elements remobilization has occurred in the VMS deposit (Cook et al, 1994;Cartwright and Oliver, 2000;Marshall et al, 2000;Gu et al, 2007;Tomkins, 2007;Theart et al, 2010;Zheng et al, 2013a;Zhang et al, 2014;Zhong et al, 2015).…”

Section: Ore Texture Evolutionmentioning

confidence: 95%

“…They are characterized by mesothermal to hypothermal temperatures, low salinities, and low CO 2 or CH 4 abundances; (4) Their mineralization depth is relatively shallow and generally less than 5 km below the ocean floor; (5) Lastly, the ore-forming metals are derived from the host rocks mostly with only negligible contribution from the upper mantle (Ulrich et al, 2002;Franklin et al, 2005). Several studies have shown that some ancient VMS deposits are strongly deformed because of their affection by orogenic process succeeding their formation, and this can lead to metal remobilization and considerable ore grade enhancement (Cook et al, 1994;Cartwright and Oliver, 2000;Marshall et al, 2000;Gu et al, 2007;Tomkins, 2007;Theart et al, 2010;Zheng et al, 2013a;Zhang et al, 2014;Zhong et al, 2015). However, the mechanism of elemental remobilization in the VMS deposits overprinted by tectono-metamorphism is not yet sufficiently understood.…”

Section: Introductionmentioning

confidence: 95%

Micro-textural and fluid inclusion data constraints on metallic remobilization of the Ashele VMS Cu-Zn deposit, Altay, NW China

Zheng

Wang

Chen

et al. 2016

Journal of Geochemical Exploration

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Applying the box plot to the recognition of footwall alteration zones related to VMS deposits in a high-grade metamorphic terrain, South Africa, a lithogeochemical exploration application

Cited by 15 publications

References 14 publications

Exploration Potential of Fine-Fraction Heavy Mineral Concentrates from Till Using Automated Mineralogy: A Case Study from the Izok Lake Cu–Zn–Pb–Ag VMS Deposit, Nunavut, Canada

Exploration Potential of Fine-Fraction Heavy Mineral Concentrates from Till Using Automated Mineralogy: A Case Study from the Izok Lake Cu–Zn–Pb–Ag VMS Deposit, Nunavut, Canada

Systematics of Hydrothermal Alteration at the Falun Base Metal Sulfide Deposit and Implications for Ore Genesis and Exploration, Bergslagen Ore District, Fennoscandian Shield, Sweden

Micro-textural and fluid inclusion data constraints on metallic remobilization of the Ashele VMS Cu-Zn deposit, Altay, NW China

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