The Cornubian ore field of southwest England is spatially associated with the roof of an S-type, ilmenite series, high heat production monzogranite batholith hosted by a deformed and lightly metamorphosed, upper Paleozoic marine mudstone-sandstone sequence. Three metallogenic stages can be recognized within the ore field: a prebatholith stage (300-400 Ma), when minor strata-bound Fe-Mn oxy-hydroxide and Fe-Cu sulfide synsedimentary deposits formed; a synbatholith stage (270-300 Ma), or main-stage event, when hydrothermal deposits of Sn-Cu-As-Fe-Zn-Pb were formed; and a postbatholith stage (Mesozoic-Cainozoic), when epithermal vein deposits of Pb, Ag, Sb, Ba, Zn, Fe, U, Go, Ni, and Au, and hydrothermal-supergene kaolinite deposits, formed.The main-stage event was related to the protracted crystallization and cooling history of the batholith. Several compositional features of the granite were important in promoting base metal mineralization, namely, (1) the Sn-rich nature of the magma, which constituted an important metal reservoir; (2) moderately reducing conditions during crystallization and (3) a peraluminous evolutionary trend, which both promoted the retention of base metals in residual melts; (4) high boron contents, which enhanced water solubility in the melt and thus increased the availability of magmatic fluid in residual magmas; and (5) high contents of heat-producing elements, which exerted a significant influence on the crystallization history of the batholith and led to the maintenance of residual melts at depth for 10 to 20 Ma after initial emplacement.Main-stage mineralization phenomena are focused on the roof and margins of the major plutons, buried ridges, and satellite stocks of a large batholith. The principal types of mineral deposit are lodes and replacement deposits containing cassiterite and Cu, As, Fe, and Zn sulfides, and sheeted greisen-bordered vein swarms containing wolframite and cassiterite with minor Sn, Cu, Fe, As, and Zn sulfides. The ore field represents a fossil plutonic (-3,000 to -4,000 m) hydrothermal system in which hot (200 degrees -500 degrees C), moderately saline (10-30 equiv wt % NaCl) fluids of mixed meteoric, magmatic, and metamorphic origin were circulating. Meteoric fluids were drawn in from the wall rocks adjacent to the batholith and convected through subvertical fractures which were concentrated along the axial trace of each compartment of the batholith. It is postulated that most of the mineralization formed where metal and sulfur-bearing fluids of essentially meteoric origin mixed with metal and sulfur-bearing fluids of magmatic departure. Convective flow was controlled by the shape and depth of the batholith and the local and regional fracture systems which constituted high permeability corridors. These fracture systems were produced by the hydraulic and tectonic expansion of faults and fractures formed prior to and during batholith emplacement and the hydraulic-tectonic expansion of cracks resulting from thermal stresses.Erosion of the batholith roof in the early Mesozoic led to an increase in epithermal activity and the superimposition of epithermal systems on the earlier plutonic hydrothermal systems. Epithermal activity continued throughout the Mesozoic and Cainozoic and a wide variety of vein mineralization, including Fe, Ba-Pb, Pb-F, Pb-Sb, U-Ni-Co-Ag-As-Bi, and Au-Se-Pb-Ag-Hg, was emplaced. Epithermal hydrothermal systems also played an important role in the development of the economically important, in situ china clay deposits. Epithermal fluids (less than 200 degrees C) had a wide salinity range (1-27 equiv wt % NaCl). Vein deposits are predominantly hosted by north-south-trending faults or extensional fractures which are often linked to north-west and north-northwest-trending wrench faults. The latter transect the peninsula and link the ore field to deep Mesozoic-Cainozoic sedimentary basins. The high heat production Cornubian batholith constituted a regional thermal anomaly throughout the Mesozoic-Cainozoic. Heated meteoric water percolated down through the granite plutons and welled up within the metasedimentary wall rocks. Fluid movement was also controlled by zones of high permeability associated with active wrench and extensional faults. Faulting also promoted movement through the ore field by the mechanism of seismic pumping. In addition, the faults may have channeled formation waters from the Mesozoic-Cainozoic sedimentary basins into the ore field. Contemporary hot spring activity atests to the continuing dynamism of the environment and highlights the superimposed complexity of hydrothermal systems associated with high heat production granite batholiths.
Late-stage volatile-rich topaz granites occur widely but sparsely throughout the southwest England Sn-Cu-polymetallic mineralized S-type biotite granite batholith. New observations from the St. Austell area have clarified field relations, and demonstrate the importance of an aureole of tourmalinization affecting both granitic and sedimentary host rocks. Topaz granite contacts are often marked by pegmatitic zones showing undirectional solidification textures and carrying vugs of quartz-tourmaline; minor intrusive sheets have symmetrical haloes of tourmalinization within adjacent host rocks. The topaz granites are mineralogically complex, containing primary topaz, zinnwaldite, or lepidolite, amblygonite (and other phosphates), and various Nb-Ta rich accessory phases, as well as...
The Sub Saharan Africa agricultural sector is one of the most disadvantaged regions, partly due to high fertiliser import costs from the northern hemisphere. Malawi is one such country which faces these fertiliser challenges for the agricultural sector growth and food crop production. However, Malawi has numerous intrusive alkaline rocks, nepheline syenites, especially within the Chilwa alkaline province. This study was therefore conducted to assess these nepheline syenites for their potential as potassium sources. We used Malawi's new airborne geophysical gamma ray data acquired in 2013, coupled with satellite remote sensing, to identify nepheline syenites suitable as possible sources for alternative silicate K-fertiliser, and carried out geochemical analysis of whole rock samples. Results show that the K2O content for the nepheline syenites varies from 3.17 wt % to 9.14 wt % with an average of 5.22 wt %. The K2O/Na2O ratio for Malawi's nepheline syenites ranges from 0.41 to 1.28 with an average of 0.65 showing that the nepheline syenites are mostly sodic but with variable composition. In addition to nepheline, the calcium feldspathoid davidsmithite ((Na,Ca)AlSiO4) was identified in the syenites using scanning electron microscopy with energy dispersive analysis. Although the different intrusive complexes are not homogenous, our results show that, generally, the nepheline syenites from Malawi have similar geochemistry and mineralogical composition to those which have been used as crushed-rock fertilisers in other parts of the world.
The reproduction of species, in particular the human species, has always been anchored in the consumption of natural resources (water, minerals, plants, etc.). Over the last two centuries, as a result of the change that the industrial revolution made to civilization, the form in which we use and appropriate natural resources has drastically altered, and the speed of consumption has grown tremendously. Some countries produce (and export) goods derived directly from the exploitation of their natural resources while other countries are consumers, although most can play both roles. Brazil is a major producer and exporter of food and agricultural and mineral commodities. This paper explores the role of this geobiodiversity giant and presents a technological path to make more efficient forms of how we use and exploit natural resources. It does so by drawing upon information from institutional sources and data from stonemeal research developed in Brazil and throughout the world. Stonemeal technology can unite the mineral and agricultural sectors since it uses crushed rocks – that are soil remineralizers – to help fertilize leached or degraded soils, also acting as a mechanism to capture atmospheric CO2, a highly useful source of help in the search for reaching UN's Sustainable Development Goals. This could improve and cheapen the costs of agricultural and forest production and reduce climate change processes.
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