The Geochronology of Tasmanian Tin Deposits Using LA-ICP-MS U-Pb Cassiterite Dating

Author:

Denholm J. L.1,Stepanov A. S.2,Meffre S.1,Bottrill R. S.3,Thompson J. M.1

Affiliation:

1. Center for Ore Deposit and Earth Sciences (CODES), Private Bag 126, University of Tasmania, Hobart, Tasmania 7001, Australia

2. Faculty of Earth Resources, Collaborative Innovation Centre for Exploration of Strategic Mineral Resources, China University of Geosciences, Wuhan 430074, China

3. Mineral Resources Tasmania, Rosny Park, Hobart, Tasmania 7018, Australia

Abstract

Abstract The island state of Tasmania is the most important tin producer in Australia. The spatial and genetic relationship between Tasmanian tin deposits and Devonian-Carboniferous granites, which intruded throughout the Tabberabberan orogeny, has long been understood. However, little geochronological data is available to link mineralization to nearby intrusions. In this study, we investigate the connection between 19 Tasmanian tin deposits and their potential source granites, using U-Pb cassiterite dating by laser ablation-inductively coupled plasma-mass spectrometry. Archean pegmatitic cassiterite was also characterized and used for the calibration of U-Pb ratios. Tin mineralization in Tasmania occurred between 391 ± 6.3 and 359 ± 7.8 Ma, which is coincident with most postorogenic granites of the Tabberabberan orogeny. In conjunction with the granite ages, cassiterite ages become younger from the east of the state to the west, and tin mineralization occurred over a protracted period spanning 32 m.y. Dating of several placer cassiterite samples produced unexpected results, such as the occurrence of 374 ± 4.7 Ma cassiterite on eastern King Island, an area known only to contain the 350 Ma Grassy granite, suggesting a distant provenance. Tasmanian cassiterite rarely shows evidence of Pb loss; however, some analyses are characterized by elevated Th and U, likely caused by microinclusions such as monazite, which may have a detrimental effect on cassiterite U-Pb dating. This study demonstrates the utility of cassiterite dating for understanding the origin of tin deposits in complex terrains with protracted periods of tin mineralization.

Publisher

Society of Economic Geologists

Subject

Economic Geology,Geochemistry and Petrology,Geology,Geophysics

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