Abstract

Mineralization is related to multiple felsic intrusions. Since mineralization is contained in fractures (>95%) rather than being disseminated Logtung is not a skarn deposit. The principal reason is that the reaction skarn host rocks, which were derived from calcareous shales interbedded with graphitic quartzites, are carbonate poor and competent. Hence, permeable mineralization formed in permeability created by hydraulic fracturing, and not by replacement. Logtung shows a scheme of several phases (4) of mineralization related to multiple intrusions which is similar to that which is so important in, for example, the evolution of the Climax and Urad-Henderson Mo systems. The Logtung Deposit shows many similarities to porphyry Mo deposits in the western Cordillera and may be classed as a porphyry W(scheelite)-Mo deposit, with a W/Mo ratio of 3.3:1.0. The principal reasons are that mineralization is spatially associated with porphyritic intrusive phases and that much of the mineralization occurs as typical porphyry-style crackle breccias.--Modified journal abstract.

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