[SRD33-P07] GRANITES FORM HAVING W-MO ORES, REE PEGMATITES, AND GEOCHEMISTRY, IMPLICATE AN FLUID ABSENT MELT CRYSTALLIZATION
Keywords:flat form, peralkaline granite, shallow depth, fluid absent melt, REE mineralization
The Khanbogd is big peralkaline pluton, in Southern Mongolia with pegmatites of high concentration of LREE. The Khanbogd pluton composed of two elliptic bodies; main and small, which are well reflected in the satellite images. Flat or laccolith in shape was determined from modeling of gravity data (Kovalenko et al, 2007). According to this model, the northern part of the pluton is the thickest (15 km) and the thickest decreases southerly to about 7 km. A recent study shows a collection of flat or sheet like intrusions in two bodies, by the interpretation of Landsat images. For example, the main body consists of four flat or semi flat intrusions. The most REE rich pegmatites are located in first arc shape like flat intrusion. In the multi-element distribution diagram the fluid absent character is observed from low of Ba, Sr and high of Pb, Th, U, Li (Batulzii, 2017). The above mentioned granites show not symmetric flat chondrite-normalized REE patterns with the strong Eu negative anomaly.
There is alkali syenite and granite pluton Ulantolgoi, in western Mongolia. The Ta-Nb-Zr concentration has estimated from alkali granite of latest phase after alkali syenite. The ferrous minerals for granite and syenite are riebeckite and biotite. The pluton also elliptic in surface same as Khanbogd pluton. The core samples logging and Ta-Nb-Zr concentration show flat form intrusions of different feeder.
The main citation to laccoliths, sills- sheets and ring dike is that those are intrusions associated with magma at shallow depths. This involves that the magma ascends along a plane of fault or bedding in host rocks and forming a relatively sheet or flattened form in direction (Petford, 2008).
That’s the pluton Khanbogd is formed by collection, at least 4 sheet like intrusions in two separate magmatic bodies, which were ascended along disk like fracture planes country rock from shallow depth magma source. High content of fluid immobile elements (Li, U, F), and low of Ba, Sr show a magma crystallization of fluid absent melting.
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