Alabama Tin Belt: Metallogenesis and Mineral Resource Evaluation. Year-End Progress Report

摘要

The Alabama Tin Belt is a 20 km long 3 km wide zone in Tallapossa County, Alabama along which tin deposits occur in veins and pegmatites associated with granitoids of the Pinckneyville Complex. Computer-based algorithms were developed to calculate granite chemistry from modal mineralogy (GRCHEM) and to calculate modal mineralogy from whole rock chemical analyses (PERANORM). In addition, fluorine abundances in Alabama Tin Belt granites and their biotites have been determined using a selective-ion electrode method. The granites contain 55-551 ppM F (average 258 ppM). Fluorine contents are highest in mafic facies of most granites and generally decrease with advancing differentiation. The fluorine concentrations in the Rockford Granite, however, increase slightly from 211 to 273 ppM with increasing SiO sub 2 contents, and remain relatively constant with increasing K sub 2 O, Rb and Ba contents. Distinctive fluorine distribution patterns of the individual plutons may be related to different degrees of biotite, muscovite and apatite crystallization. The fluorine concentrations in Alabama Tin Belt granites, pegmatites and associated tin ores are generally lower than those (> 500 ppM) reported from granites of other tin provinces. This suggests that fluorine may not have been a significant component of the mineralizing fluids, and that other complexing agents, such as CO sub 2 , derived by oxidation of graphitic country rocks, may have dominated the ore-forming fluids. 29 references, 10 figures, 12 tables. (ERA citation 09:041578)