Greisen Research Articles

Nb-Ta oxides as recorders of hydrothermal activity in the Shihuiyao Rb-Nb-Ta-(Be-Li) deposit, Inner Mongolia, NE China

The Nb-Ta ore body in the Shihuiyao Rb-Nb-Ta-(Be-Li) deposit comprises muscovite-albite granite (MAG) and greisen (GR), with the dominant Nb-Ta minerals of columbite-group minerals (CGM) and ixiolite. The petrographic and chemical data suggest that the Nb-Ta oxides well record the magmatic-hydrothermal evolution process. The magmatic CGM are generally homogenous crystals or with oscillatory zoning patterns, while the CGM formed during the magmatic-hydrothermal transition stage overprints the early CGM crystals in the MAG or shows a normal zoning pattern (decreasing Nb/Ta ratios from the core to rim) in the GR, and possesses higher contents of Sc and Ti. The hydrothermal Nb-Ta oxides in both the MAG and GR share the same origin, i.e., the hydrothermal fluids exsolved from the magma at the late stage of magmatic evolution. However, distinct chemical differences between them indicate that a single fluid activity did not pervade the entire system; instead, two different hydrothermal processes were present: fluid metasomatism and water–rock reaction. The hydrothermal CGM generally occurs in the GR and metasomatizes the primary crystals by a coupled dissolution-reprecipitation mechanism. The chemical compositions of these CGM grains were significantly modified during this process, which was manifested by the increasing Sn and W contents in the reprecipitated phases. The ixiolite is most likely formed by another hydrothermal mechanism, i.e., water–rock reaction, during which the hydrothermal fluids can extract a large amount of Sn, Sc, U, and REE from the wall rocks or earlier formed magmatic phases and finally controlled the formation and chemical distribution of the ixiolite.

Spatiotemporal distribution, geological characteristics and metallogenic mechanism of tungsten and tin deposits in China: An overview

Tungsten and tin are important strategic and critical mineral resources, as well as one of China’s most abundant mineral resources. Their distribution is mainly concentrated in the South China block, followed by the Kunlun-Qilian-Qinling-Dabie orogenic belt, the Tianshan-Xingmeng orogenic belt, and the Tibet-Sanjiang orogenic belt. The tungsten and tin resources in South China are mainly concentrated in the Nanling tungsten-tin metallogenic belt, the northern Jiangxi-southern Anhui tungsten metallogenic belt, the Youjiang-Guibei tin metallogenic belt, and the southeast coastal tungsten-tin metallogenic belt. The formation of tungsten and tin deposits in China spans a large period of time, from Proterozoic to Cenozoic, but the Mesozoic Yanshanian mineralization is the most important. There are five main types of primary tungsten-tin deposits in China, namely, porphyry, greisen, skarn, quartz vein, and cassiterite-sulfide. In addition, there are also other types such as altered granite, hydrothermal breccia, and low-temperature hydrothermal vein. Many tungsten-tin deposits are often not of a single genetic type, and multiple mineralization types commonly co-exist in a deposit. Most of the granitoids associated with tungsten mineralization are thought to be S-type granite derived from partial melting of continental crustal materials, while the granitoids associated with tin deposits include I-type and A-type in addition to the S-type granite. Crust-mantle interaction plays an important role in generation of the Sn-bearing granites. Nd-Hf isotope studies show that beside the Sn-bearing granites, some W-bearing granites also have mantle-derived contributions. Whether it is W-bearing or Sn-bearing granite, a highly evolved feature is often more favorable for mineralization. The composite granitoids in South China are closely related to multiple tungsten-tin mineralization. Many tungsten and tin deposits in China are often co-produced with mineralization of other rare metals. According to the combination of ore elements, they mainly include the following three types: W-(Sn)-Be (including Sn-Be), W-(Sn)-Nb-a (including Sn-Nb-Ta), and Sn-Li-Rb-Nb-Ta. All of them are closely related to highly evolved peraluminous granites. The source of ore-forming fluids in most tungsten-tin deposits is closely related to magmatic hydrothermal activity, and some deposits also have characteristics of multi-source fluids. The temperature and salinity of ore-forming fluids vary widely, and the composition of the fluid system is also complex in many cases. Oxygen fugacity plays an important role in the transportation and precipitation of tin, but such an effect on tungsten is still in debate. The formation of many tungsten-tin deposits is generally controlled by a number of factors, such as temperature dropping, fluid mixing, fluid immiscibility, fluid boiling, and water-rock interaction.

Obituary of Kenneth I. Greisen

Obituary of Kenneth I. Greisen

DISTRIBUIÇÃO E ASPECTOS METALOGENÉTICOS DAS OCORRÊNCIAS DE SCHEELITA NO PRÉ-CAMBRIANO DO ESTADO DE MINAS GERAIS, BRASIL

This paper presents a general description of six scheelite mineralized areas in Minas Gerais State,southeastern Brazil:- Nazareno - São João Del Rei - Lagoa Dourada area where scheelite occurs confined to orthoamphibolitic rocks of the Barbacena Greenstone Belt;- Iron Quadrangle area where most scheelite occurrences are related to a auriferous shear zones of theNova Lima Group of the Rio das Velhas Greenstone Belt;Itinga - Coronel Murta - Rubelita area in the Araçuai Fold Belt where scheelite is present in calcsilicaterocks interlayered with metasedimentary schists of the Macaubas Group and in quartz vein withwolframite;- Galiléia-Mendes Pimentel area in Costeiro Fold Belt where scheelite mineralization occurs in calcsilicatelayers and quartz veins, in schists of the São Tomé Group;- Itamonte - Itanhandu area in the Ribeira Fold Belt where scheelite is related to greisen of leucocraticgranitoids cupolas;- Rio Manhuaçu - Mutum area in the Costeiro Folded Belt where the scheelite mineralization ispresent in calc-silicate xenoliths associated with granitic rocks of the Pocrane Complex.

Dating and Nd, Sr, O Isotope Studies of the Chaganhundi Granite

The crust in northern Xinjiang intensely moved about during the Middle Hercynian, which formed a large area of granitoid. In the south of Alataw Mountain, granitic bodies such as Kongwusayi, Wulasitan, Zuluhong, Kazibieke and Chaganhundi are distributed along the Bole W-Sn mineralization belt from east to west, of which the Zuluhong, Kazibieke and Chaganhundi granitic bodies in the west sector are directly related to W-Sn mineralizations of quartz vein type, greisen type and chlorite type in this area. The

Greisen and associated mineralization at Silvermine, Missouri

Greisen and associated mineralization at Silvermine, Missouri

Topaz from Cornwall, with an account of its localities

Topaz, so common an accessory in tin lodes in all parts of the world, has hitherto been looked upon as comparatively rare in Cornwall. When massive, or even in the form of small, well-developed crystals, it is a mineral easily overlooked, or apt cursorily to be mistakcn for quartz.The presence of topaz as a microscopic accessory in granite, greisen, and rarely elvans, from most of the Cornish masses, has been determined by Dr. J. S. Flett in the course of the work of the Geological Survey; while the late Mr. J. H. Collins was responsible for the record of other interesting localities.In the present notes I have collected all the available information respecting its mode of occurrence and localities ; and have added several new ones, at some of which the mineral occurs in considerable mass, thus affording evidence that topaz is in Cornwall, as in the case of other countries, a comparatively common associate of cassiterite and wolframite, both in granite and sedimentary rocks.