Gahnite in the metamorphosed stratiform massive sulfide deposits of the Mineral District, Virginia, U.S.A.

Sandhaus, D. J.; Craig, James R.

doi:10.1007/bf01140841

Cited by 12 publications

(15 citation statements)

References 17 publications

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“…Gahnite and staurolite have been identified as indicator minerals for ,metamorphosed massive sulfide deposits elsewhere (Sandhaus and Craig, 1986;Spry and Scott, 1986a, b;Spry et al, 2000). Gahnite is an accessory mineral in the altered rocks at Falun, preferably occurring in QA rock in close vicinity to the massive sulfides.…”

Section: Mineral Chemical Datamentioning

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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Section: Mineral Chemical Datamentioning

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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“…In view of the spatial relationship between zincian spinel and metamorphosed volcanogenic base-metal sulfide mineralization, and based on compositional considerations, zincian spinel has been proposed as a potential exploration guide in the search for ores of this type (Sandhaus & Craig 1982, Ririe & Foster 1984, Sheridan & Raymond 1984, Spry & Scott 1986a, b, Spry 2000, Spry et al 2000, Walters 2001, Walters et al 2002. The importance of this relationship is demonstrated by the spatial association of zincian spinel with some of the world's largest massive sulfide deposits, including Broken Hill and Cannington (Australia), and Aggeneys (Namaqualand, South Africa), as well as with many other smaller base-metal sulfide occurrences in, for example, the Appalachian and Scandinavian Caledonides (Spry & Scott 1986b), the Linda deposit, Canada (Zaleski et al 1991), and the Mamandur deposit, India (Chattopadhyay 1999).…”

Section: Introductionmentioning

confidence: 99%

Zincian Spinel Associated With Metamorphosed Proterozoic Base-Metal Sulfide Occurrences, Colorado: A Re-Evaluation of Gahnite Composition as a Guide in Exploration

Heimann

Spry

Teale³

2005

The Canadian Mineralogist

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Zincian spinel [(Zn,Fe,Mg)Al 2 O 4 ] is an accessory mineral in a variety of rock types, in particular, metamorphosed massivesulfide deposits, pegmatites, aluminous metasedimentary rocks, skarns, marbles, and sulfide-bearing granulites. Textural and compositional studies of zincian spinel in thirteen Proterozoic sulfide deposits metamorphosed to the amphibolite and granulite facies in Colorado, many of which are spatially associated with Mg-rich alteration zones, shed new light on the use of zincian spinel composition as a guide to sulfide ores. Zincian spinel from the Independence, Bon Ton, and Sedalia deposits and some cases from the Green Mountain, Betty, Caprock, Cinderella, and Cotopaxi deposits show compositions that correspond to zincian spinel associated with metamorphosed massive-sulfide deposits hosted by hydrothermally altered Fe-Al-rich metasedimentary and metavolcanic rock units elsewhere in the world (Gahnite 44-90 Hercynite 0-45 Spinel 0-25). However, other compositions of zincian spinel from these last five deposits and from three locations in the Wet Mountains (Marion and Amethyst prospects and an unnamed prospect) are depleted in Zn and enriched in Mg and Fe. These examples of Mg-rich zincian spinel occur in rocks in or adjacent to metamorphosed massive sulfides dominated by Mg-rich minerals such as phlogopite, anthophyllite, gedrite, tremolite, forsterite, cummingtonite, sapphirine, cordierite, enstatite, and clinohumite. The composition of zincian spinel in and surrounding metamorphosed massive-sulfide deposits is influenced by reactions involving Zn and Fe sulfides, as well as by bulk-rock composition, which in the case of many metamorphosed massive-sulfide deposits in Mg-rich alteration zones in Colorado, causes a marked enrichment in the spinel component of zincian spinel, to Gahnite 0-65 Hercynite 0-50 Spinel 25-90. Knowledge of the geological setting must be considered when using zincian spinel as a guide to metamorphosed massive-sulfide deposits.

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“…Gahnite is stable over a wide range of oxygen-and sulfur fugacities. At higher ƒO 2 , gahnite coexists with magnetite, whereas it is associated with Fe-rich silicates and pyrrhotite at lower ƒO 2 (Sandhaus and Craig, 1986). At the Izok Lake deposit, pyrrhotite inclusions in chalcopyrite, and chalcopyrite replacement by magnetite indicate that GRD-Mag and pyrrhotite did not form simultaneously.…”

Section: Magnetite In Bedrock Samplesmentioning

confidence: 88%

The surface texture and morphology of magnetite from the Izok Lake volcanogenic massive sulfide deposit and local glacial sediments, Nunavut, Canada: Application to mineral exploration

Makvandi

Beaudoin

McClenaghan

et al. 2015

Journal of Geochemical Exploration

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Gahnite in the metamorphosed stratiform massive sulfide deposits of the Mineral District, Virginia, U.S.A.

Cited by 12 publications

References 17 publications

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

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

Zincian Spinel Associated With Metamorphosed Proterozoic Base-Metal Sulfide Occurrences, Colorado: A Re-Evaluation of Gahnite Composition as a Guide in Exploration

The surface texture and morphology of magnetite from the Izok Lake volcanogenic massive sulfide deposit and local glacial sediments, Nunavut, Canada: Application to mineral exploration

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