Geology of the Hog Mountain tonalite and associated lode gold deposits, Northern Alabama Piedmont: Final report for the 1986-1987 project year
The Hog Mountain tonalite intrudes lower Paleozoic graphitic phyllites of the Wedowee formation and is transgressed by a series of planar, en echelon, bifurcating, auriferous quartz-sulfide veins with well-defined sericite-sulfide alteration envelopes. Least-altered tonalite is white, medium-grained, and weakly to non-foliated. It is characterized by moderately uniform distributions of quartz and oscillatory-normal zoned plagioclase (An/sub 7-41/), with minor amounts of biotite, muscovite, ilmenite, apatite, zircon and corroded garnet; K-feldspar is rare. Least-altered granitoids are peraluminous (A/CNK > 1.15), exhibit significant major- and trace-element variations, are characterized by relatively low REE contents, and have moderately high /delta//sup 18/O (+9.7 to +11.2 %) and uniform /delta/D (-82 to -78 %) values. Biotite log (X/sub Mg//X/sub Fe/)-log(X/sub F//X/sub OH/) relations suggest contamination of an I-type granitic melt by graphitic metapelites. Corroded garnets (Pyr/sub 3/Alm/sub 55/Spess/sub 17/Gross/sub 25/) within the granitoids are chemically-similar to euhedral garnets in adjacent schists and in fine-grained, foliated plagioclase-biotite-muscovite-ilmenite xenoliths, and were probably derived from the metasedimentary host rocks. Equilibration conditions of the xenolith mineral assemblages (465-510/degree/C at ca. 6 kb), calculated using garnet-biotite-muscovite-plagioclase thermobarometry, are similar to inferred metamorphic P-T conditions of underthrusting of Wedowee metasediments to mid-crustal levels during Paleozoic crustal thickening. Observed chemical variations may be modeled by plagioclase/biotite-controlled fractionation of a peraluminous tonalitic melt, accompanied by local cumulus mineral-intercumulus liquid segregation and graphitic metapelite contamination during emplacement. 70 refs., 20 figs.
- Research Organization:
- Alabama Univ., University (USA). Dept. of Geology
- OSTI ID:
- 6855296
- Report Number(s):
- UA-8013748; ON: TI88013748
- Country of Publication:
- United States
- Language:
- English
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