|
Galina Pavlova, Institute of Geology and Mineralogy (Russian Federation)
Alexander Borisenko, Institute of Geology and Mineralogy (Russian Federation)
Alexander Obolenskiy, Institute of Geology and Mineralogy (Russian Federation)
Alexey Travin, Institute of Geology and Mineralogy (Russian Federation)
|
|
New age data from a belt of ore Ag-Sb, Cu-Ag-Hg-Sb and Sb-Hg deposits is considered to be a metallogeny specific of intracontinental areas with mafic and granitic magmatism related to mantle plumes. In the ore district of the SE Altai-NW Mongolia, situated in Delyuno-Yustid back arc rift basin, Devonian sedimentary volcanic and terrigenous rocks are intruded by Upper Devonian - Lower Carboniferous granites, pre-granitic mafic intrusions, post-granite gabbro-diabase and diabase porphyry dikes and younger lamprophyry dikes (245-236 Ma, Ar-Ar, biotite) of the Chuisky complex. Ag-Sb mineralization of the Yustid ore cluster are of Early Mesozoic age - 240 ±1.6 Ma)(Ar-Ar, sericite). These ages show that the Ag-Sb mineralization are temporally associated with the emplacement of the lamprophyres. The age of lamprophyre dike hosting a siderite vein is 243±2.5 Ma (Ar-Ar, biotite).
The Cu-Ag-Hg-Sb mineralization is dated at 234.4±1.0 Ma; the Sb-Hg mineralization is the youngest in this district (231.5±1.0 Ma, Ar-Ar, sericite). A gradual change of Ag-Sb (siderite-tetrahedrite) ore to complex Cu-Ag-Hg-Sb (Hg-Ag-tetrahedrite) and Sb-Hg (cinnabar, sulfosalts and stibnite) mineralization along deep faults is interpreted as due to the development of a zonation in the distribution of ore deposits along the main ore-controlling structures. A similar sequence of endogenous events is observed in the SE Pamir: monzogabbro, monzodiorite, granite (114-107 Ma, Rb-Sr); rare-metal granite (96.9±6.6 Ma, Rb-Sr, biotite) and (98±4 Ma, Ar-Ar); topaz-protolithionite and ongonite dikes + Sn-W greisen ore (98.5-97.5±1 Ma, Ar-Ar, muscovite); Ag-Sb mineralization (45±0.5 Ma, Ar-Ar, sericite); Cu-Ba-Hg mineralization. In addition, Paleogene-Neogene alkaline mafic dikes and overlying subvolcanic bodies consisting of trachy-andesitobasalts, trachytes, shoshonites and rhyolites are known in this district. As in many areas Sn and Ag deposits occur in the same ore cluster and their zonal distribution around magmatic center is well established with Ag-Sb mineralization being related to the postmagmatic stage of granitic intrusion.
It appears that the Ag-Sb deposits were formed much later than Sn deposits, and age of Ag-Sb ore is close to the age of alkaline mafic dikes. The same trend of alkaline-mafic and granitic magmatism and related Sn-sulfide, Ag-Sb and Hg mineralization has been established for other Ag regions of Asia (Kirgizia, Yakutia). The genetic link of hydrothermal Ag-Sb mineralization with alkaline mafic magmatism related to mantle plumes is supported by geochronological and isotope (3He/4He) data. These data also suggest that the duration and unidirectionality of the development of Sn-Ag mantle-crustal systems are associated with centers of mafic and alkaline mafic melts derived from the deep mantle and crustal (intermediate) centers of granitoid magmas. Supported by RFBR grants 06-05-64789, 07-05-00803, by grant of Ministry for Russian Science and Education DSP.2.1.1.702.
|
