Geochronology and Trace Element Characteristics of Pyrite from Selected Carbonate Hosted Pb-Zn Ore Deposits
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Abstract
Carbonate-hosted ore deposits, such as Mississippi Valley-type (MVT), and Irish-type deposits, are a major class of Pb-Zn ores. Due to the mineralogy of these deposits, numerical constraints on the timing of mineralization are few. This thesis investigates pyrite Re-Os geochronology for dating of ore formation, supplemented by a study of trace elements in pyrite. The two major deposits studied are the Lisheen deposit from Ireland, and the Nanisivik deposit from Nunavut. At Lisheen, different models of formation have been proposed, based upon ore formation ages of either ~ 345 Ma or ~ 280 Ma. The new Re-Os data show that Lisheen formed between 340 - 355 Ma in a primarily syngenetic/syndiagenetic fashion, and discount the significant of a ~ 280 Ma paleomagnetic age as a primary ore-forming event. The Re-Os pyrite geochronology from Nanisivik confirms it is a rare example of a Precambrian MVT deposit, forming at approximately 1100 Ma.