W. David Sinclair | USGS Science

USGS1998

International strategic mineral issues summary report– Tungsten

Scheelite and wolframite are the principal minerals currently mined for tungsten. Both occur in hard-rock deposits; wolframite is also recovered from placer deposits. Most current mine production of tungsten is from vein/stockwork, skarn, porphyry, and strata-bound deposits. Minor amounts are produced from disseminated, pegmatite, breccia, and placer deposits. Most tungsten is used to make tungsten carbide and tungsten alloys for use in machine tools and drilling equipment. Other important applications are in lamp filaments and cathodes, high-speed steels, textile dyes, paints, and catalysts. The world is well endowed with tungsten resources. China and the former Soviet Union have 8 of the world's 10 largest deposits; these 8 contain about half of the world's resources of tungsten. If economic conditions are suitable, world tungsten resources in known deposits and their extensions (categories R1 and R2), including economic, marginal, and subeconomic resources, are sufficient to permit world production to continue at 1995 levels until well into the 21st century. World tungsten resources in identified deposits and districts that are currently economically exploitable (category R1E) appear to be sufficient to meet world demand at 1995 levels only until the year 2007. However, the figure for resources of this kind does not include or reflect resources whose economic parameters are unknown in major producing areas in the former Soviet Union, China, and other nonmarket-economy countries and thus severely underestimates future tungsten availability. In 1995, China and the former Soviet Union accounted for over three-fourths of the world's mine production of tungsten. China alone produced about two-thirds of world output. Given its vast resources, China will likely maintain its prominent role in world tungsten supply. By the year 2020, changes in supply patterns are likely to result from declining output from individual deposits in Australia, Austria, and Portugal and the opening of new mines in Canada, China, and the United Kingdom.

Circular↗

USGSDate not supplied

Exsolved magmatic fluid and its role in the formation of comb-layered quartz at the Cretaceous Logtung W-Mo deposit, Yukon Territory, Canada

Comb-layered quartz is a type of unidirectional solidification texture found at the roofs of shallow silicic intrusions that are often associated spatially with Mo and W mineralisation. The texture consists of multiple layers of euhedral, prismatic quartz crystals (Type I) that have grown on subplanar aplite substrates. The layers are separated by porphyritic aplite containing equant phenocrysts of quartz (Type II), which resemble quartz typical of volcanic rocks and porphyry intrusions. At Logtung, Type I quartz within comb layers is zoned with respect to a number of trace elements, including Al and K. Concentrations of these elements as well as Mn, Ti, Ge, Rb and H are anomalous and much higher than found in Type II quartz from Logtung or in igneous quartz reported elsewhere. The two populations appear to have formed under different conditions. The Type II quartz phenocrysts almost certainly grew from a high-silica melt between 600 and 800°C (as β-quartz); in contrast, the morphology of Type I quartz is consistent with precipitation from a hydrothermal solution, possibly as α-quartz grown below 600°C. The bulk compositions of comb-layered rocks, as well as the aplite interlayers, are consistent with the hypothesis that these textures did not precipitate solely from a crystallising silicate melt. Instead, Type I quartz may have grown from pockets of exsolved magmatic fluid located between the magma and its crystallised border. The Type II quartz represents pre-existing phenocrysts in the underlying magma; this magma was quenched to aplite during fracturing/degassing events. Renewed and repeated formation and disruption of the pockets of exsolved aqueous fluid accounts for the rhythmic banding of the rocks.

Yukon Territory↗