PRE-ORE AMPHIBOLITE AND GRANITES IN THE LITHIUM CORPORATION OF AMERICA (LCA) MINE, BESSEMER CITY, NORTH CAROLINA
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).