The Watershed tungsten deposit (NE Queensland, Australia): Scheelite vein mineralization, alteration and mineral chemistry (original) (raw)
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Economic Geology, 2021
The Watershed tungsten deposit (49.2 Mt avg 0.14% WO3) lies within the Mossman orogen, which comprises deformed Silurian-Ordovician metasedimentary rocks of the Hodgkinson Formation intruded by Carbonif-erous-Permian granites of the Kennedy Igneous Association. The Hodgkinson Formation in the Watershed area comprises skarn-altered conglomerate, psammite, and slate units that record four deformation events evolving from ductile, isoclinal, colinear folding with transposition (D1-D3) to brittle ductile shear zones (D4). Multiple felsic to intermediate dikes cut across the metasedimentary rocks at Watershed including: (1) Car-boniferous, monzonite dikes (zircon U/Pb age of 350 ± 7 Ma) emplaced during D1-2; and (2) Permian granite plutons and dikes (zircon U/Pb ages of 291 ± 6, 277 ± 6, and 274 ± 6 Ma) and diorite (zircon U/Pb age of 281 ± 5 Ma) emplaced during D4. Tungsten mineralization is largely restricted to skarn-altered conglomerate, which preserves a peak metamorphic mineralogy formed during ductile deformation and comprises garnet (Grt40-87 Alm0-35Sps1-25Adr0-16), actinolite, quartz, clinopyroxene (Di36-59Hd39-61Jhn1-5), and titanite. A first mineraliza-tion event corresponds to the crystallization of disseminated scheelite in monzonite dikes (pre-D3) and adjacent units, with scheelite grains aligned in the S1-2 fabric and affected by D3 folding. This event enriched the Hodgkinson Formation in tungsten. The bulk of the scheelite mineralization formed during a second event and is concentrated in multistaged, shear-related, quartz-oligoclase-bearing veins and vein halos (muscovite 40 Ar-39 Ar weighted average age of 276 ± 6 Ma), which were emplaced during D4. The multistage veins developed preferentially in competent, skarn-altered conglomerate units and formed synchronous with four retrograde alteration stages. The retrograde skarn minerals include clinozoisite after garnet, quartz, plagioclase, scheelite, and phlogopite with minor sodium-rich amphibole, which formed during retrograde stages 1 and 2, accompanied by later muscovite, calcite, and chlorite formed during retrograde stage 3. Retrograde stage 4 was a late-tectonic, noneconomic sulfide stage. The principal controls on scheelite mineralization at Watershed were the following: (1) early monzonite dikes enriched in scheelite; (2) D4 shear zones that acted as fluid conduits transporting tungsten from source areas to traps; (3) skarn-altered conglomerate lenses that provide a competent host to facilitate vein formation and a source for calcium to form scheelite; and (4) an extensional depo-sitional environment characterized by vein formation and normal faulting, which provide trapping structures for tungsten-bearing fluids, with decompression being a likely control on scheelite deposition. The coexistence of scheelite with oligoclase in monzonite dikes and veins suggests that tungsten was transported as NaHWO 4 0. Exploration in the area should target Carboniferous monzonite, associated with later syn-D4 shear zones cutting skarn-altered conglomerate.
2019
Tungsten is considered a strategic metal by various countries, including Australia. Between 1998 and 2016 Australia has been steadily increasing its tungsten production, but it is still far smaller than those of the main producers (e.g., China, Russia). Watershed with its current resources of 49.2 Mt averaging 0.14% WO3 is considered one of the biggest undeveloped tungsten deposits outside of China, and if developed would boost Australia’s tungsten production. We will be presenting the geological, geochemical and structural characteristics of the Watershed deposit, as well as the timing, mineral paragenesis and fluid characteristics of the mineralizing system; with the main goal of improving our understanding of the Watershed tungsten deposit and how to explore for similar deposits in northeast Queensland.
International Symposium on "Dawn of a New Natural History - Integration of Geoscience and Biodiversity Studies". 5-6 March 2004. Sapporo, Japan. Tungsten analyses were made on 16 samples collected from the North Miyako granitic body in Northeast Japan. Petrographic facies of the North granitic body vary from quartz diorite in the marginal zone (zone A), to tonalite and granodiorite (zone B), and to granite in the central zone (zone C). A large number of barren and scheelite-bearing aplitic veins are distributed around the Yamaguchi deposit which occurs in the contact aureole of zone C granite. The tungsten content of zone C granite is lower than that of the granitic rocks in zones A, B and the aplitic veins. It appears that tungsten in the differentiated granitic magma, which was associated with ore mineralization, was transported out of the magma chamber by magmatic fluids. The tungsten content is generally low in the North Miyako granitic rocks but high in granitic rocks...