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The Mineralization and Zoning at East Midway, Near Bourke, N.S.W. Geology of the Everton Molybdenite Field

出版	La Trobe University, 1982
URL	http://books.google.com.hk/books?id=3BDFPQAACAAJ&hl=&source=gbs_api

註釋Part A. Regional metamorphism has caused reaction between interbedded carbonate and minor pelite material at East Midway. The result is a recrystalized calcite marble with interstitial diopside. Later, hydrothermal fluids, rising through open fractures above an underlying, crystalizing, volatile rich, 'A' type granite (S.S.) magma, intersected this marble, diopside unit forming a granular, andradite rich garnet, skarn. Surrounding units of interbedded pelite and carbonate were richer in the pelite component. These had also partly reacted and recrystalized during regional metamorphism, and were now replaced by reaction of the hydrothermal fluids, to a banded skarn unit. Banding is relic bedding of the carbonate and pelites. Fluid over pressure, developed by CO2 evolved from skarn forming reactions, caused brittle fracture of the pelitic schist country rocks. Ca rich fluids permeated these fractures causing alteration of the pelites to a calcsilicate assemblage. Calcsilicate replacment (alteration) is most intense close to the skarn units and it decreases outwards to moderate and weak in the foot wall and hanging wall of the deposit. Calcsilicate replacement extends for up to 100 metres into the foot wall and hanging wall. Minor tin mineralization has formed as tin bearing andradite rich garnet in the granular skarn. No cassiterite is present at East Midway and the deposit is uneconomic.