Pb-Pb and U-Pb Dating of Cassiterite by In Situ LA-ICPMS: Examples Spanning ~1.85 Ga to ~100 Ma in Russia and Implications for Dating Proterozoic to Phanerozoic Tin Deposits

This paper investigates applicability of cassiterite to dating ore deposits in a wide age range. We report in situ LA-ICPMS U-Pb and Pb-Pb dating results (n = 15) of cassiterite from six ore deposits in Russia ranging in age from ~1.85 Ga to 93 Ma. The two oldest deposits dated at ~1.83–1.86 Ga are rare metal Vishnyakovskoe located in the East Sayan pegmatite belt and tin deposits within the Tuyukan ore region in the Baikal folded region. Rare metal skarn deposits of Pitkäranta ore field in the Ladoga region, Fennoscandian Shield are dated at ~1.54 Ga. Cassiterite from the Mokhovoe porphyry tin deposit located in western Transbaikalia is 810 ± 20 Ma. The youngest cassiterite was dated from the deposits Valkumei (Russian North East, 108 ± 2 Ma) and Merek (Russian Far East, 93 ± 2 Ma). Three methods of age calculations, including 208Pb/206Pb-207Pb/206Pb inverse isochron age, Tera-Wasserburg Concordia lower intercept age, and 207Pb-corrected 206Pb*/238U age were used and the comparison of the results is discussed. In all cases, the dated cassiterite from the ore deposits agreed, within error, with the established period of magmatism of the associated granitic rock.

The Mechanisms Forming the Five–Floor Zonation of Quartz Veins: A Case Study in the Piaotang Tungsten–Tin Deposit, Southern China

It is common among many vein–type tungsten deposits in southern China that the thickness of ore veins increases from <1 cm to >1 m with increasing depth. A five–floor zonation model for the vertical trend of vein morphology was proposed in the 1960s and has been widely applied for predicting ore bodies at deeper levels, but the causative mechanisms for such a zonation remain poorly understood. The Piaotang tungsten–tin deposit, one of the birthplaces of the five–floor zonation model, is chosen as a case study for deciphering the mechanisms forming its morphological zonation of quartz veins. The vertical trend of vein morphology and its link to the W–Sn mineralization in Piaotang was quantified by statistical distributions (Weibull distribution and power law distribution) of vein thickness and ore grade data (WO3 and Sn) from the levels of 676 m to 328 m. Then, the micro–scale growth history of quartz veins was reconstructed by scanning electron microscope–cathodoluminescence (SEM–CL) imaging and in situ trace element analysis. The Weibull modulus α of vein thickness increases with increasing depth, and the fractal dimensions of both vein thickness and ore grade data (WO3 and Sn) decrease with increasing depth. Their vertical changes indicate that the fractures that bear the thick veins were well connected, facilitating fluid focusing and mineralization in mechanically stronger host rocks. Three generations (Q1–Q3) of quartz were identified from CL images, and the CL intensity of quartz is possibly controlled by the concentrations of Al and temperature. From the relative abundance of the Q1–Q3 quartz at different levels, the vertical trend of vein morphology in Piaotang was initially produced during the hydrothermal event represented by Q1 and altered by later hydrothermal events represented by Q2 and Q3. Statistical distributions of vein thickness combined with SEM–CL imaging of quartz could be combined to evaluate the mineralization potential at deeper levels.

Magmatic-Hydrothermal Mineralization Processes at the Yidong Tin Deposit, South China: Insights from In Situ Chemical and Boron Isotope Changes of Tourmaline

Owing to the superimposition of water-rock interaction and external fluids, magmatic source signatures of ore-forming fluids for vein-type tin deposits are commonly overprinted. Hence, there is uncertainty regarding the involvement of magmatic fluids in mineralization processes within these deposits. Tourmaline is a common gangue mineral in Sn deposits and can crystallize from both the magmas and the hydrothermal fluids. We have therefore undertaken an in situ major, trace element, and B isotope study of tourmaline from the Yidong Sn deposit in South China to study the transition from late magmatic to hydrothermal mineralization. Six tourmaline types were identified: (1) early tourmaline (Tur-OE) and (2) late tourmaline (Tur-OL) in tourmaline-quartz orbicules from the Pingying granite, (3) early tourmaline (Tur-DE) and (4) late tourmaline (Tur-DL) in tourmaline-quartz dikelets in the granite, and (5 and 6) core (Tur-OC) and rim (Tur-OR), respectively of hydrothermal tourmaline from the Sn ores. Most of the tourmaline types belong to the alkali group and the schorl-dravite solid-solution series, but the different generations of magmatic and hydrothermal tourmaline are geochemically distinct. Key differences include the hundredfold enrichment of Sn in hydrothermal tourmaline compared to magmatic tourmaline, which indicates that hydrothermal fluids exsolving from the magma were highly enriched in Sn. Tourmaline from the Sn ores is enriched in Fe3+ compared to the hydrothermal tourmaline from the granite and displays trends of decreasing Al and increasing Fe content from core to rim, relating to the exchange vector Fe3+Al–1. This reflects oxidation of fluids during the interaction between hydrothermal fluids and the mafic-ultramafic wall rocks, which led to precipitation of cassiterite. The hydrothermal tourmaline has slightly higher δ11B values than the magmatic tourmaline (which reflects the metasedimentary source for the granite), but overall, the tourmaline from the ores has δ11B values similar to those from the granite, implying a magmatic origin for the ore-forming fluids. We identify five stages in the magmatic-hydrothermal evolution of the system that led to formation of the Sn ores in the Yidong deposit based on chemical and boron isotope changes of tourmaline: (1) emplacement of a B-rich, S-type granitic magma, (2) separation of an immiscible B-rich melt, (3) exsolution of an Sn-rich, reduced hydrothermal fluid, (4) migration of fluid into the country rocks, and (5) acid-consuming reactions with the surrounding mafic-ultramafic rocks and oxidation of the fluid, leading to cassiterite precipitation.

Mineral Resource Depletion Assessment: Alternatives, Problems, Results

The depletion of non-renewable natural resources (primarily mineral and energy resources) and its assessment is a problem that is analyzed based on the concept of sustainable development. Mineral resource depletion assessment is particularly important for resource-based economies. It provides for assessing the impact of mineral asset disposal that results from the suspension or termination of operations conducted by a mining company due to insurmountable circumstances. The results of such an event will be manifested at the national, regional, and local levels and felt by mining companies, suppliers, workers, the population of the territory, and other stakeholders. The study clarifies the attributes and essence of mineral resource depletion, analyzes the advantages and limitations of the existing tools for assessing mineral resource depletion, identifies depletion factors, describes a methodology for assessing mineral resource depletion, and contains a case study of a tin deposit. The results of the study contribute to the development of the theory on the depletion of non-renewable natural resources. They provide for assessing losses to social wellbeing that can be caused by stopping the use of profitable mineral reserves.