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present and there have been at least four major episodes of economic mineralisation. Significant mineral deposits include Proterozoic magnetite, silica, dolomite and magnesite deposits; Cambrian VHMS base metal-Au and ultramafic-related Pt-group minerals (PGM) and chromite deposits; Devonian orogenic and intrusion related Au deposits; Middle Devonian-Tournaisian granite-related Sn, W, fluorite, magnetite, Ag-Pb-Zn and Ni deposits; Triassic coal and Oligocene-Miocene lignite deposits; and Cenozoic alluvial Au, Sn and PGM deposits, and residual Ni-Co, Fe oxide, silica and clay deposits. Resource data are listed in Table 1. This contribution is abbreviated from Seymour et al., (2006; revised 2007), but updated. Cambrian Orogenesis, ultramafics, the Arthur Lineament and associated mineralisation The major collisional Tyennan Orogeny occurred between c. 512-506 Ma (Turner et al., 1998), contemporaneous with the first phase Tasmania contains a broad variety of economic mineral deposits, which includes several that have been known for over a century and are still operating today or were worked in the recent past. The Arthur Lineament, a belt of allochthonous amphibolite, carbonate rocks, psammite and pelite in northwest Tasmania hosts the Savage River magnetite deposit, which is now considered to be a Proterozoic carbonate replacement deposit with affinities to Kiruna-style iron-oxide Cu-Au deposits. The allochthon was formed during an early Cambrian collisional event between an east-facing passive margin sequence and an intraoceanic island arc. Post collisional, proximal submarine volcanism at c. 500 Ma in the Mount Read Volcanics followed and associated mineralisation includes world-class deposits. High grade Zn-Pb-Au-Ag-Cu massive sulfide deposits (e.g., Rosebery and Hellyer) were formed from seawater-dominated hydrothermal fluids. Disseminated Cu-Au-Ag deposits of the Mount Lyell field are associated with broad alteration zones that include phyllosilicate assemblages indicative of a component of oxidised magmatic fluid, as does the Henty Au deposit in the north. Orogenic Au is an important deposit style in northeast Tasmania and includes the Tasmania deposit, Australia's largest single Au reef. Largely post-orogenic granitic magmatism (Lower Devonian-Tournaisian) includes an important Sn-Wbase metal±magnetite mineralising event associated with reduced, fractionated granite in northeast and western Tasmania. World class Sn±Cu sulfide skarn and vein deposits are the product of interpreted magmatic fluids exsolved from these granitic magmas. The highly unusual disseminated Avebury Ni deposit is associated with granite of this type. World class scheelite skarn deposits on King Island lie in the contact aureole of moderately oxidised, unfractionated Tournaisian granodiorite on King Island.

The Boco prospect is a large, fault dismembered, pipelike, hydrothermally altered zone in the Mount Read Volcanics of western Tasmania. It is a synvolcanic alteration zone hosted by felsic volcanic rocks formed in a subaqueous proximal intracaldera setting. Previous detailed geochemical and geophysical surveys and extensive drill testing have indicated it contains no economic metals.The strong to intense, pervasively quartz + phyllosilicate + pyrite-altered northern segment of the prospect is semiconcentrically zoned. Short wavelength infrared (SWIR) spectral analysis has revealed that phyllosilicate assemblages grade from phengitic white mica in the least altered peripheries, through normal potassic white mica, to central zones containing kaolinite, slightly sodic white mica, and pyrophyllite. Mass balance calculations indicate average net mass losses in the altered facies were about 10 to 30 g/100 g, mainly owing to loss of SiO2, which implies very high hydrothermal water-rock ratios. Whole-rock oxygen isotope compositions of the enclosing least altered felsic rocks (δ 18 O values 8.2-11.7‰) are indistinguishable from those of altered facies (9.6-11.8‰). We attribute the former to low-temperature diagenetic isotopic exchange with 0 per mil δ 18 O seawater in the peripheral least-altered zones, and the latter to exchange with 3 to 6 per mil δ 18 O hydrothermal fluids at high water/rock ratios and temperatures generally greater than 220°C, and locally greater than 270°C, in the intensely altered facies. Pyrite sulfur isotope compositions in the Boco altered facies (δ 34 S values 1.2-7.2‰) are distinctly lower than most Tasmanian massive sulfide deposits (6-15‰), compatible with a dominantly magmatic source of sulfur.The alteration mineral assemblages, estimated mass changes, and isotopic data show that the Boco alteration system was formed by a large volume of focused acidic hydrothermal fluid which had an oxygen isotope composition of 3 to 6 per mil δ 18 O at and temperature greater than 270°C. The slightly 18 O-enriched fluid isotope composition suggests derivation from either mixed magmatic fluid and seawater or isotopically evolved seawater. Its advanced argillic altered facies place Boco among a newly recognized class of southeast Australian Cambrian volcanic-hosted prospects and deposits. These include Chester, Basin Lake, Western Tharsis, and North Lyell in Tasmania, and Rhyolite Creek, Hill 800, and Mike's Bluff in eastern Victoria. SWIR spectral analyses with field-portable spectrometers allow early discrimination of this type of hydrothermally altered system, and can potentially assist subsequent exploration in mapping facies zonation.

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