Origin of the Dashuigou Independent Tellurium Deposit at the Southeastern Qinghai-Tibet Plateau:Based on the Abundances of Trace Elements in the Country Rocks

Through a detailed study of the abundances and spatial-temporal distribution patterns of Te,Bi,As,Se,Cu,Pb,Zn,Au,and Ag in the rock types of different geological epochs in the Dashuigou independent tellurium deposit,and in combination with other research findings of previous researchers in this area,the authors conclude as follows:Abundances of the main ore-forming elements Te,Bi,As,Se,Au,and Ag are not high in the regional geological background,generally lower or close to their respective crustal Clark values,but almost all altered country rocks contain high levels of ore-forming elements.This indicates that the deposit’s ore-forming elements do not come from the country rocks.This also indicates that the geological thermal events that cause alteration and mineralization originate from depths and may be related to mantle plumes.Considering the distribution pattern of these ore-forming elements in the ore bodies’hanging wall and footwall,the metallogenic mechanism may be as follows:Mineralization is not achieved through lateral secretion in the horizontal or near horizontal direction,but rather through the upward movement and emplacement of deep ore-forming elements driven by geological processes such as mantle plumes.In addition,the migration of deep ore-forming elements is not achieved through dispersed infiltration between overlying rock particles,but through non widespread concentrated penetrating channels.This type of channel is likely to be the expansion structures where faults from different directions intersect,or where linear faults intersect with circular structures.

Geochemical and Boron Isotopic Evidence that Tourmaline Records Country Rock Assimilation of Leucogranites in the Himalayan Orogen

Tourmaline geochemical and boron(B)isotopic compositions in two-mica granites(TMG),tourmaline-bearing leucogranites(Tou-LG),tourmalites and metapelites from the Gyirong-Malashan areas of the Himalayan orogen provide evidence for country rock assimilation during the intrusion of Himalayan leucogranite.The schorls in Gyirong leucogranitic plutons show low contents of MgO(0.238%-1.160%)and δ^(11)B values(-12.1‰--11.2‰),while dravites gathered in the contact zone between the leucogranitic veins and metapelites show high contents of MgO(4.815%-6.755%)and δ^(11)B values(-10.7‰--9.3‰).This geochemical and isotopic variation of tourmalines can also be identified in the Malashan gneiss dome.As a result,three types of tourmaline were identified in the Himalayan orogen:(1)Tou-Ⅰ in the TMG and Tou-LG,which is the most common tourmaline type of schorl;(2)Tou-Ⅱ(dravite and high-Mg schorl)in the Tou-LG and tourmalite at the margins of the leucogranite;and(3)Tou-Ⅲ(mainly dravite,with minor high-Mg schorl)in metapelites of the High Himalayan Crystalline Sequence.The lenses and veins of Tou-LG may have experienced metasomatism and assimilation as a result of interaction with the High Himalayan Crystalline Sequence metasedimentary country rocks,which can be traced by the geochemical and isotopic characteristics of the tourmaline therein.

Constraining the Timing of the Molopo Farms Complex Emplacement and Provenance of Its Country Rock

The Molopo Farms Complex(MFC)is a 13000 km2layered,mafic-ultramafic intrusion straddling the southern border of Botswana with South Africa.It does not outcrop due to Cenozoic cover,but is believed to intrude the