Minor elements in sphalerite and their implications for metallogenesis of carbonate-hosted zinc-lead deposits of the Yukon Territory and adjacent district of Mackenzie
Creators: name: McLaren, Graeme Peter
Publisher: name: University of British Columbia
Year: 2010

description: Minor element concentrations in sphalerite from the newly discovered carbonate-hosted zinc-lead deposits in the Yukon Territory and adjacent District of Mackenzie have been determined to define the metallogeny of this remote region of the Canadian cordillera. Concentrations of silver, cadmium, cobalt, copper, iron, manganese, nickel, lead, and mercury in sphalerite were analyzed in 166 specimens from 48 deposits; an additional 13 elements were investigated at a qualitative level. Minor element data defines two ages of regional metallogeny; different mineralizing processes also might be represented by these two events. Sphalerite in the northern cordillera is generally enriched in copper, lead, and mercury, and depleted in iron, relative to other districts containing similar zinc-lead deposits. Iron contents vary sympathetically with darkness of colour in sphalerite. Minor element variations within single hand specimens, and analytical variations, are both insignificant relative to between-specimen variations, as revealed by analyses of variance. Minor element variations within single deposits are small relative to between-deposit variations; therefore, each deposit is characterized by the minor element assemblage of the sphalerite it hosts. Regionally, sphalerite occurrences in carbonate host rocks (dominantly dolomites) occurs as breccia matrix, vein, and fracture fillings. Two major age groups of host rocks, Proterozoic to Lower Cambrian, and Middle Ordovician to Devonian, are separated by an Upper Cambrian to Middle Ordovician unit that is bounded by unconformities and is relatively barren of mineral occurrences. Linear regression analysis of minor element results indicates distinctly different trends for each age group. Probability graph analysis of all minor element contents define bimodal distributions consisting of relatively 'enriched' and 'depleted' populations for most elements. Geographic distributions of sphalerite 'enriched' in minor elements correlate consistently with geographic distributions of Proterozoic and Lower Cambrian host rocks. Sphalerite 'depleted' in minor elements occurs dominantly in Ordovician to Devonian host rocks. A single period of sphalerite deposition is inadequate to explain the observed minor element patterns. Two distinct minor element populations correlating in geographic distribution with two separate age groups of host rocks indicate that at least two independant metallogenic events led to the sphalerite mineralization. A major shale basin, likely dewatering to produce metal-rich brines, is associated only with the Ordovician to Devonian hosts, whereas major unconformities and paleophysiographic elements suggestive of karstic environments are associated with the Proterozoic and Lower Cambrian hosts. A regional interpretation suggests that these different features might be responsible for the different minor element concentrations outlined. Therefore, a model of two metallogenic events, one during Middle to Late Cambrian, and another during Late Devonian or later, is proposed to explain the spatial and temporal relations between minor element populations and host age distributions of sphalerite deposits in carbonate rocks of the northern cordillera.