Geology of the Hog Mountain tonalite and associated lode gold deposits, Northern Alabama Piedmont: Final report for the 1986-1987 project year

Technical Report · Mon Feb 01 00:00:00 EST 1988

OSTI ID:6855296

Green, N L; Lesher, C M

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

Related Subjects

58 GEOSCIENCES
GOLD
DEPOSITS
ALABAMA
GEOCHEMISTRY
GEOLOGY
HISTORICAL ASPECTS
MINERALOGY
PETROGRAPHY
PROGRESS REPORT
STABLE ISOTOPES
STRATIGRAPHY
CHEMISTRY
DOCUMENT TYPES
ELEMENTS
FEDERAL REGION IV
ISOTOPES
METALS
NORTH AMERICA
TRANSITION ELEMENTS
USA
580100* - Geology & Hydrology- (-1989)
580300 - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580400 - Geochemistry- (-1989)