Iron and chlorine as guides to stratiform Cu-Co-Au deposits, Idaho Cobalt Belt, USA

Nash, J. Thomas; Connor, Jon J.

doi:10.1007/bf00196334

Cited by 21 publications

(19 citation statements)

References 19 publications

(10 reference statements)

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“…The paragenesis of these high-salinity inclusions is uncertain, however (see Landis and Hofstra, 2012). Additional evidence for saline hydrothermal fluids comes from very Cl rich compositions of biotite within the biotitite lenses (up to 1.87 wt % Cl), which in unmineralized zones typically contain abundant marialitic scapolite (Connor, 1990;Nash and Connor, 1993); scapolite also occurs within siliciclastic strata of the Apple Creek Formation several kilometers east of the Blackbird district and more widely in the coeval Yellowjacket Formation (Tysdal and Desborough, 1997;Tysdal, 2003).…”

Section: Nature Of the Hydrothermal Fluidsmentioning

confidence: 97%

“…These so-called "biotitites," which form strata-bound lenses up to 1 m thick, consist mainly of dark green Cl-rich Fe biotite with lesser quartz, albite, microcline, garnet, and/or chloritoid, plus minor disseminated cobaltite or other sulfide minerals (Nash and Hahn, 1989;Nash and Connor, 1993;Bookstrom et al, 2007). Distal to the sulfide deposits, the biotitites locally contain porphyroblasts of marialitic (Na-Cl) scapolite (Connor, 1990;Nash and Connor, 1993). Early studies by Nash and Hahn (1989) used petrographic and geochemical data on the biotitites to infer a major component of alkaline mafic igneous tuff, but more recent work by A.A. Bookstrom and S.E.…”

Section: Deposits Of the Blackbird Districtmentioning

confidence: 98%

“…On this basis, F-bearing hydrothermal fluids are proposed for this early mineralizing event; hence, the Y, REEs, and Be in the deposits could have been transported by F complexes, as widely inferred for mineralogically similar deposits elsewhere (Gieré, 1996, and references therein). Lack of F-rich biotite in the wall-rock biotitites (Nash and Connor, 1993;J.F. Slack, unpub.…”

Section: Nature Of the Hydrothermal Fluidsmentioning

confidence: 99%

“…Gangue minerals are principally quartz and Cl-rich Fe biotite (Nash and Connor, 1993), accompanied by lesser chlorite, muscovite, garnet, tourmaline, and/or chloritoid. Fluorapatite is locally abundant in the Brown Bear deposit, forming disseminated anhedral grains, together with cobaltite, in Clrich Fe biotite; the F-rich nature of the fluorapatite was determined by electron microprobe (H.E.…”

Section: Strata-bound Fe-co-cu-au-bi-y-ree Deposits Of the Idaho Cobamentioning

confidence: 99%

“…Based on petrographic and geochemical criteria such as elevated LREEs, Nash and Hahn (1989) interpreted these distinctive strata as metamorphosed alkaline mafic tuffs. Given the presence of abundant marialitic scapolite in biotitite units distal from the deposits (Nash and Connor, 1993), other possible protoliths include evaporites and brine pool accumulations. However, recent geochemical data obtained on these biotitites-including for immobile trace elements and REEs-instead suggest they represent metamorphosed alteration zones in which Fe-and Cl-rich hydrothermal fluids reacted with aluminous clastic sediments to form abundant Clrich Fe biotite (A.A. Bookstrom and S.E.…”

Section: Origin Of the Biotitites And Related Quartzose Lensesmentioning

confidence: 99%

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Strata-Bound Fe-Co-Cu-Au-Bi-Y-REE Deposits of the Idaho Cobalt Belt: Multistage Hydrothermal Mineralization in a Magmatic-Related Iron Oxide Copper-Gold System

Slack

2012

Economic Geology

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Mineralogical and geochemical studies of strata-bound Fe-Co-Cu-Au-Bi-Y-rare-earth element (REE) deposits of the Idaho cobalt belt in east-central Idaho provide evidence of multistage epigenetic mineralization by magmatic-hydrothermal processes in an iron oxide copper-gold (IOCG) system. Deposits of the Idaho cobalt belt comprise three types: (1) strata-bound sulfide lenses in the Blackbird district, which are cobaltite and, less commonly, chalcopyrite rich with locally abundant gold, native bismuth, bismuthinite, xenotime, allanite, monazite, and the Be-rich silicate gadolinite-(Y), with sparse uraninite, stannite, and Bi tellurides, in a gangue of quartz, chlorite, biotite, muscovite, garnet, tourmaline, chloritoid, and/or siderite, with locally abundant fluorapatite or magnetite; (2) discordant tourmalinized breccias in the Blackbird district that in places have concentrations of cobaltite, chalcopyrite, gold, and xenotime; and (3) strata-bound magnetite-rich lenses in the Iron Creek area, which contain cobaltiferous pyrite and locally sparse chalcopyrite or xenotime. Most sulfide-rich deposits in the Blackbird district are enclosed by strata-bound lenses composed mainly of Cl-rich Fe biotite; some deposits have quartz-rich envelopes.Whole-rock analyses of 48 Co-and/or Cu-rich samples show high concentrations of Au (up to 26.8 ppm), Bi (up to 9.16 wt %), Y (up to 0.83 wt %), ΣREEs (up to 2.56 wt %), Ni (up to 6,780 ppm), and Be (up to 1,180 ppm), with locally elevated U (up to 124 ppm) and Sn (up to 133 ppm); Zn and Pb contents are uniformly low (≤821 and ≤61 ppm, respectively). Varimax factor analysis of bulk compositions of these samples reveals geochemically distinct element groupings that reflect statistical associations of monazite, allanite, and xenotime; biotite and gold; detrital minerals; chalcopyrite and sparse stannite; quartz; and cobaltite with sparse selenides and tellurides. Significantly, Cu is statistically separate from Co and As, consistent with the general lack of abundant chalcopyrite in cobaltite-rich samples.Paragenetic relations determined by scanning electron microscopy indicate that the earliest Y-REE-Be mineralization preceded deposition of Co, Cu, Au, and Bi. Allanite, xenotime, and gadolinite-(Y) commonly occur as intergrowths with and inclusions in cobaltite; the opposite texture is rare. Monazite, in contrast, forms a poikiloblastic matrix to cobaltite and thin rims on allanite and xenotime, reflecting a later metamorphic paragenesis. Allanite and xenotime also show evidence of late dissolution and reprecipitation, forming discordant rims on older anhedral allanite and xenotime and separate euhedral crystals of each mineral. Textural data suggest extensive deformation of the deposits by folding and shearing, and by pervasive recrystallization, all during Cretaceous metamorphism. Sensitive high resolution ion microprobe U-Pb geochronology by Aleinikoff et al. (2012) supports these paragenetic interpretations, documenting contemporaneous Mesoproterozoic growth of early xenotime and ...

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