Modes of occurrence of tungsten in alluvial soils and river sediments in the area of the Grantcharitsa tungsten deposit, Western Rhodopes, Bulgaria

A distinct increase in the concentration of W in the topsoil (from 19–20 to 71 ppm) is found in the vertical profile of the alluvial soil at the Grantcharitsa deposit. The distribution of W, Fe, and C is well correlated, which indicates a significant role of organic material and iron oxides/hydroxides formed in the soil in the chemical behavior of W. The role in these processes of scheelite, W-containing goethite and rutile identified in the soil is insignificant.

Fluid Evolution and Ore Genesis of the Juyuan Tungsten Deposit, Beishan, NW China

The newly discovered Juyuan tungsten deposit is hosted in Triassic granite in the Beishan Orogen, NW China. The tungsten mineralization occurred as quartz veins, and the main ore minerals included wolframite and scheelite. The age, origin, and tectonic setting of the Juyuan tungsten deposit, however, remain poorly understood. According to the mineralogical assemblages and crosscutting relationships, three hydrothermal stages can be identified, i.e., the early stage of quartz veins with scheelite and wolframite, the intermediate stage of quartz veinlets with sulfides, and the late stage of carbonate-quartz veinlets with tungsten being mainly introduced in the early stage. Quartz formed in the two earlier stages contained four compositional types of fluid inclusions, i.e., pure CO2, CO2-H2O, daughter mineral-bearing, and NaCl-H2O, but the late-stage quartz only contained the NaCl-H2O inclusions. The inclusions in quartz formed in the early, intermediate, and late stages had total homogenization temperatures of 230–344 °C, 241−295 °C, and 184−234 °C, respectively, with salinities no higher than 7.2 wt.% NaCl equiv (equivalent). Trapping pressures estimated from the CO2-H2O inclusions were 33−256 MPa and 36−214 MPa in the early and intermediate stages, corresponding to mineralization depths of 3–8 km. Fluid boiling and mixing caused rapid precipitation of wolframite, scheelite, and sulfides. Through boiling and inflow of meteoric water, the ore-forming fluid system evolved from CO2-rich to CO2-poor in composition and from magmatic to meteoric, as indicated by decreasing δ18Owater values from early to late stages. The sulfur and lead isotope compositions in the intermediate-stage suggest that the Triassic granite was a significant source of ore metals. The biotite 40Ar/39Ar age from the W-bearing quartz shows that the Juyuan tungsten system was formed at 240.0 ± 1.0 Ma, coeval with the emplacement of granitic rocks at the deposit. Integrating the data obtained from the studies including regional geology, ore geology, biotite Ar-Ar geochronology, fluid inclusion, and C-H-O-S-Pb isotope geochemistry, we conclude that the Juyuan tungsten deposit was a quartz-vein type system that originated from the emplacement of the granites, which was induced by collision between the Tarim and Kazakhstan–Ili plates. A comparison of the characteristics of tungsten mineralization in East Tianshan and Beishan suggests that the Triassic tungsten metallogenic belt in East Tianshan extends to the Beishan orogenic belt and that the west of the orogenic belt also has potential for the discovery of further quartz-vein-type tungsten deposits.

Genesis of the Yingzuihongshan Tungsten Deposit, Western Inner Mongolia Autonomous Region, North China: Constraints from in Situ Trace Elements Analyses of Scheelite

In situ analyses of trace elements and rare-earth elements (REEs) were performed by use of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on scheelite samples from the Yingzuihongshan tungsten deposit in western Inner Mongolia Autonomous Region, China. The contents of trace elements Nb, Ta and Mo of scheelite indicate that the ore-forming fluid is magmatic hydrotherm and is exsolved from highly fractionated granitic melt. The scheelite has high REE contents and ∑REE values, and a very inhomogeneous distribution of REEs exists in different scheelite grains or even in one scheelite grain. The cathodoluminescence (CL) images of scheelite grains display well-developed zoning or fine oscillatory zoning. Development of zoning is closely related to the variable contents of REEs, and the darkness of shade of CL images are mainly determined by ∑REE values, but they have no correlation with the distribution patterns of REEs. The chondrite-normalized REE distribution patterns of scheelite are classified as the middle REEs (MREEs)-enriched type, except for a strong negative Eu-anomaly, which could be a REE-flat type and or a MREEs-depleted type. Trace element composition of scheelites from the Yinzuihongshan tungsten deposit reflect that the ore-forming materials mainly came from the crust and the ore-forming fluids are dominantly derived from the granitic magma in an oxidizing environment, in which very dynamic conditions of the hydrothermal system prevailed during precipitation of scheelite. On the basis of the above understanding and field geological featured, we considered that the Yingzuihongshan tungsten deposit is the quartz-vein-hosted tungsten type that is genetically associated with monzonitic granite.

Beneficiation Studies of the Low-Grade Skarn Phosphate from Mactung Tungsten Deposit, Yukon, Canada

A preliminary beneficiation study of low-grade skarn phosphate rocks from Mactung tungsten deposit, along the Yukon and Northwest Territories border in Canada, was carried out through standard Bond Work Index, grinding test and laboratory batch flotation tests. The skarn phosphate sample assayed 12.65% P2O5 (about 30% apatite), 31.71% CaO and 35.46% SiO2. The main gangue minerals included calcite, quartz, calc-silicates, amphibole, feldspar, and pyrrhotite. The sample had a Bond Work Index of 19.04 kWh/t, belonging to a hard ore category. The beneficiation study of the skarn phosphate sample was carried out using “direct–reverse flotation” method. The direct flotation was carried out using sodium carbonate, sodium silicate solution (water glass) and sodium oleate. Sulfuric acid and phosphoric acid were used in the reverse flotation of the carbonate gangue. One phosphorous rougher flotation, one bulk cleaner flotation and one carbonate reverse flotation at ore grind size of 86% passing 53 µm led to a phosphate concentrate assaying 28.68% P2O5, 12.06% SiO2, 0.72% MgO and 46.98% CaO, at a P2O5 recovery of 70.9%.