Title: Formation of tourmaline-rich gem pockets in miarolitic pegmatites
Abstract: AssrRAcr Analysis of fluid inclusions in spodumene, beryl, tourmaline, and quartz from miarolitic pegmatites ofAfghanistan, coupled with lithium aluminosilicate stability relations and with previous studies from gem pegmatites of San Diego County, California, indicate that pocket development in tourmaline-rich, miarolitic rare-element pegmatites occurs between approximately 475 and, 425C and between 2800 and 2400 bars. This range of P and ?r is comparable to the conditions of late-stage crystallization in geochemically similar massive (nonmiarolitic) pegmatites. Whether gem pockets form may be dependent largely on the timing of tourmaline crystallization. Formation of tourmaline removes an alkali borate component from residual pegmatitic melt, with the consequent deposition of other alkali aluminosilicate and oxide-forming minerals and exsolution of copius amounts of HrO. If tourmaline crystallization is inhibited until the late stages of pegmatite consolidation, the large quantities of HrO that are liberated may form pegmatitic pockets. IxrnonucrroN
Publication Year: 1986
Publication Date: 1986-04-01
Language: en
Type: article
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Cited By Count: 101
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