Hydrothermal alteration of mafic metavolcanic rocks and genesis of Fe-Zn-Cu sulfide deposits, Stone Hill District, Alabama

Abstract

Fe-Zn-Cu sulfide mineralization in the Stone Hill district of the northern Alabama Piedmont is hosted by zones of felsic schist and garnet schist within the Ketchepedrakee Amphibolite. The felsic schist is characterized by quartz-pyrrhotite-biotite-muscovite-plagioclase-rutilesphalerite _ chalcopyrite _ pyrite _ hornblende _ epidote assemblages and the garnet schist is characterized by garnet-hornblende-quartz-biotite-pyrrhotite-chalcopyrite _ sphalerite _ pyrite _ chlorite _ actinolite _ calcite assemblages. Both schists are well banded and highly deformed. The felsic schist locally contains ellipsoidal, polycrystalline aggregates of quartzfeldspar-biotite that superficially resemble sedimentary clasts but clearly formed tectonically by boudinage of felsic bands. The following petrographic and geochemical data and field relationships suggest that both schists are hydrothermally altered basalt (the precursor of the Ketchepedrakee Amphibolite): (1) the felsic and garnet schist units are very localized lenses (<l-km strike length, <50-m thickness); (2) contacts between the felsic schist and the amphibolite are normally gradational and may be transitional through the garnet schist; (3) both schists contain abundant rutile, distributed in the same way as ilmenite in the schists and the amphibolite; (4) the two schists and the amphibolite are uniformly enriched in compatible transition elements such as So, Ti, V, Cr, and Co; (5) ratios of incompatible, high field-strength elements such as Y, Zr, Nb, REE, and Hfare virtually identical in the schists and the amphibolite; and (6) the schists and the amphibolite exhibit similar fiat chondrite-normalized rare earth element (REE) abundance patterns (with variable Eu anomalies). Textural data indicate that alteration and mineralization of the basaltic protolith predated metamorphism and deformation. The Fe-Zn-Cu sulfide deposits in the Stone Hill district are interpreted to have formed by synvolcanic hydrothermal alteration in an incipiently rifted basin.

Petrogenesis of Triassic granitoids in the East Kunlun Orogenic Belt, northern Tibetan Plateau and their tectonic implications

“…% ilmenite and 29.2 wt. % plagioclase (Niu and Lesher, 1991); (5) the mineral/melt partition coefficients (Kd) used are from the Geochemical Earth Reference Model (http://earthref.org/KDD/ and cf., Niu and O'Hara, 2009). (Fig.…”

“…(b) Although the Nd and Hf isotopes deviate from the mantle array and A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 28 seem to be "decoupled", the Sr-Nd-Hf isotopes can be well modeled by mixing of the Paleo Tethys MORB and the old continental material in the study area. plagioclase (Niu and Lesher, 1991). The mineral partition coefficients are from the Geochemical Earth Reference Model (http://earthref.org/KDD/).…”

Geochemistry and tectonic setting of basaltic volcanism, northern Coast Mountains, southeastern Alaska

“…High field-strength elements (HFSE; e.g., Y, Zr, REE) and some first-period transition metals (e.g., Ti, V, Cr), however, are likely to have limited mobility in many geological environments (Wood et al, 1976;Pearce and Norry, 1979;Bartley, 1986;Lesher et al, 1986;Niu and Lesher, 1991). Moderate to strong covariations between Zr and other elements, such as Hf, Nd, and to a lesser extent Th, suggest that these elements were not extremely mobile during Coast Mountains metamorphism.…”

Effects of decarbonation on elemental behaviors during subduction-zone metamorphism: Evidence from a titanite-rich contact between eclogite-facies marble and omphacitite

“…(1) (TiO2 + SiO2 + CaCO3 => CaTiSiO5 + CO2; Niu and Lesher, 1991) Furthermore, the lithological contact has been proposed to preferentially serve as the major conduit for the fluid flow (Breeding et al, 2003; Fig. 7).…”