Southeastern Section - 60th Annual Meeting (23–25 March 2011)

Paper No. 58
Presentation Time: 5:30 PM-8:00 PM


CAMERON, Christopher1, THOMPSON, James2, MAXWELL, Abigail A.2, POWELL, Julie A.2, DUPONT, Ashley2, GESUALDO, Anthony M.2, CHOI, Na Hyung2, MALESKI, Jacqueline2, FLEISHER, Christopher J.2 and SWANSON, Samuel E.2, (1)Dept. of Geography, University of Georgia, Athens, GA 30602, (2)Dept. of Geology, University of Georgia, Athens, GA 30602,

Spodumene-bearing pegmatites occur in the tin-spodumene belt of North Carolina. Two large, open-pit mines (operated by Foote Mineral and LCA) mined spodumene from these pegmatites in the 1950's to 1990's (both mines are now closed). Samples of granitic rocks collected from the LCA mine in 1985 reveal ore-bearing pegmatites (see abstract by Cameron et al, this meeting) and barren intrusions, both hosted by amphibolite. The purpose of this study is to use the mineralogy of the amphibolite and barren pegmatites as a guide to mineralization.

Pre-ore (barren) granitoid rocks include a pre- and post-tectonic suite of sill-like intrusions. The pre-tectonic granitoids contain an assemblage of medium-grained Pl+Qtz+Ms+Grt enclosed in a fine-grained matrix of Pl+Qtz producing a mortar texture. A group of post-tectonic granitoid sills also lack spodumene. These rocks have a seriate textrure formed by Pl+Qtz+Bt or Pl+Kfs+Qtz+Bt+Ms.

Mineral compositions determined by electron microprobe reveal differences between the pre- and post-tectonic granitoid intrusions. Fine-grained Pl in the pre-tectonic sills is end-member albite (Ab: 99.1 to 99.7), but coarser-grained Pl is less albitic (Ab: 95.4 to 96.2). Post-tectonic rocks contain fine to medium-grained uniformly albitic (Ab: 98.2 to 99.4) Pl and Ksp (Ab: 3 to 5). Muscovite contains a modest celadonite component (pre-tectonic: FeOt+MgO = 2.7 to 3.8 wt %; post-tectonic: 1.4 to 4.2 wt % FeOt+MgO). Biotite is Fe-rich (mg# 13 to 37) with moderate levels of F (3.2 % F). Garnet is a Fe-Mn solid solution (Alm+Sps = 86 to 91 mole %).

Amphibolite (Hbl+Pl"Bt) mineral compositions are uniform: amphibole is magnesio-hornblende (mg # 58 to 65), Pl is unzoned and ranges from Ab 57 to Ab 67, Bt has a small range of Fe-Mg (mg# 52 to 54).

Mineral assemblages and the deformation pattern of the pre-tectonic barren granitic rocks are similar to the Toluca quartz monzonite. Ages and mineral assemblages of the post-tectonic barren granitic rocks are similar to the Cherryville quartz monzonite (Kish, 1977), a large pluton just to the west of the tin-spodumene belt. Relations between the barren granites and the ore granites are discussed in the paper by Stander (et al, this meeting).