Fluctuations in Graphitization of Coal Seam-Derived Natural Graphite upon Approaching the Qitianling Granite Intrusion, Hunan, China

The Lutang graphite deposit in Chenzhou, Hunan province, China, is a well-known coal seam-derived graphite (graphite formed from coal during its natural evolution) deposit with proven reserves of 9.5 million tons and prospective reserves of around 20 million tons (2015 data). The graphite occurs at an andalusite bearing sericite quartz chlorite metamorphic mudstone around a c. 530 km2 Qitianling granite intrusion. A set of coal seam-derived graphite samples from the Lutang graphite deposit in Hunan was examined by geochemical, crystallographic, and spectroscopic techniques to assess changes in the degree of graphitization approaching the intrusion. The carbon content, degree of graphitization, and Raman spectral parameters of series coal seam-derived natural graphite samples show a fluctuating increase with increasing proximity to the granite intrusion. The profile of geological structural features has a close spatial correlation with the variations in the degree of graphitization of series coal seam-derived natural graphite, and a strain-enhanced graphitization model is proposed. Moreover, the geographical distribution and the degree of graphitization are positively related to changes in the iron content of chlorite, suggesting a graphitization process promoted by mineral catalysis during metamorphism. A close spatial relationship exists between graphite mineral and chlorite occurrences when approaching the intrusive mass. The results of this research are important for understanding the role of tectonic stress and mineral catalysis on the genesis of coal-derived graphite.

Subsurface Sediment Deposits of Tanjung Berikat Coast, Bangka, Determined from GPR Interpretation

Tanjung Berikat Coast in Central Bangka, is a part of the Southeast Asian tin belt. We conducted four Ground-Penetrating Radar (GPR) survey lines and 13 hand auger coring to understand sediment deposition and composition. Two similar units were determined from GPR lines BLG 01–BLG 03: Unit A at the top part, reflected by parallel and continuous reflector configuration, weak–strong electromagnetic wave. Underneath Unit A is Unit B, characterized by subparallel configuration, not continuous–chaotic, weak–medium electromagnetic wave. Unit B is absent in BLG 04. We identify another two units from BLG 04 and BLG 03, Unit C, characterized by subparallel reflector configuration, not continuous– chaotic, weak–strong electromagnetic wave. It exhibits distinctive modulating contact with Unit D. Unit D is characterized by chaotic reflector configuration, relatively stronger electromagnetic wave that might be correlated to the granite intrusion Tanjung Klabat. Sediment deposit is composed of fine–coarse sand, consisting mostly of clastic plutonic and clastic biogenic (coral and mollusk fragments), which increase downward. This indicates marine-fluvial influence, which suggests that sea-level changes strongly influence sedimentation process. Unit A from GPR is correlated to these sediment deposits, the other three units might be correlated to weathering of older insitu deposit.

Geochemistry of Granitoids in Central Sumatra: An Identification of Plate Extension during Triassic

Previous investigations of granitoids in Sumatra were focused on age dating with minimum geochemistry composition analysis. The purpose of this study is to define the geochemistry classification of the intrusions in central Sumatra and to explain the rocks' correlation to Southeast Asia tectonic activities. A polarizing microscope was used for petrography description while XRF and ICP-MS were applied for geochemistry measurements. According to the geochemistry, almost all of the intrusions are the I-type volcanic arc granitoids. The oldest studied rock is the Late Permian Ombilin Granite that should have been formed before West Sumatra and West Burma move away from the Cathaysia. Sulit Air Granite and Tanjung Gadang Granite intrusion were triggered by the subduction of Meso-Tethys beneath West Sumatra while Lassi Pluton and Lolo Pluton due to Indo-Australia and West Sumatra convergency. The Triassic Sijunjung Granite depicts A-type granite natures to suggest an extension in the West Sumatra plate.

The Akhunovo–Petropavlovsk Granitoid Area as a Continental-Margin Center of the Long-Term Mantle–Crust Interaction: The Role of Subductional and Rift–Plume Sources

—The Akhunovo–Petropavlovsk area of the late Paleozoic granite magmatism is located in the northeast of the Magnitogorsk megazone (MMZ) in the South Urals. It is a series of successively intruded rocks (Petropavlovsk, Akhunovo, Karagai, and Uiskii Bor intrusions) differing not only in composition, the depth of formation, and ore content but also in the relationship with magmatic and fluid sources and in magma generation mechanisms. This area differs significantly in the number and composition of intrusive complexes from the igneous rocks and ore associations in the central and western parts of the MMZ. The granite magmatism pulses alternated with the collisional shearing/spreading and rifting stages. The Petropavlovsk mesoabyssal granite intrusion (347.0 ± 8.6 Ma) formed at the early stage of the area evolution. Its rocks are similar in composition to a suprasubductional series (melting products of a mantle source enriched not only in water fluid but also in Cl). Later (310–306 Ma), at the collision–compression stage, crustal intrusion of the Akhunovo–Karagai granodiorite–granite complex took place. The intruded rocks are similar to the Middle Urals continental-margin gabbro-tonalite–grano-diorite–granite plutons (320–290 Ma) bearing large gold–sulfide–quartz deposits (Berezovskoe etc.). At the final stage of the area evolution, during the transition from continental-margin regime to hard collision between the East European and Kazakhstan continents (late Carboniferous) and the intense shearing/spreading deformations, the Uiskii Bor granosyenite–granite intrusion (304.0 ± 4.8 Ma) rich in K and HFSE formed. Granite intrusions of this type have been revealed in the MMZ for the first time. Thus, the granitoid complexes of the Akhunovo–Petropavlovsk area formed under changes in geodynamic settings and are characterized by different compositions, depths of occurrence, and genesis. This permits us to consider the area a typical continental-margin center of the long-term mantle–crust interaction, where magma generation proceeded at different mantle and crust levels, with the participation of both suprasubductional and enriched plume-related rift sources.

EVALUATING GEOCHEMISTRY OF RARE EARTH ELEMENTS IN COPPER DEPOSIT OF AGHBOLAGH, NORTH OF OSHNAVIEH, WEST AZARBAIJAN PROVINCE-IRAN

AghBolagh region is located in southwest of West Azarbaijan Province that is 10 km far from north of Oshnavieh. Most of the rocky outcrops in the region include Cambrian deposits (carbonate deposits and clastic deposits (sandstone and shale)). These deposits were later influenced and altered by granite Intrusion. The Intrusion is made of granite and in term of nature, it is magmatic with High-potassium calc-alkaline and peralumin. Also the penetration of intrusion and Ore maker solvent in further distances from the contact point and inside the sequences of sandstone has formed quartzite rocks and ore bearing veins of cooper. The REE pattern normalized to Chondrite for granite, skarn, and marble intrusion and vein deposits shows the fact that, although the REEs pattern is a little smooth and unified, LREEs have more enrichment compared to HREEs in different lithology. The range of normalized numbers to Chondrite in AghBolagh deposit is clearly variable (2.58 to 141.93 for La and 0.14 to 27.27 for Yb). This indicates that there have been clear differences in increase and decrease of LREEs and HREEs during the formation of AghBolagh deposit stones and rocks. The La / Y ratio shows the pH condition of the environment for formation of deposit. This ratio in AghBolagh deposit ranges from 0.09 to 2.26. The granite intrusion shows the most amount of La/Y which is equal to 2. Skarn Zone (Endoskarn and Exoskarn and Ore in Exoskarn) shows two different conditions. The first condition: the part in which LA/Y>1, and this can be observed in samples near the intrusion and Skarn ore is also found in this range. The second condition: the part that La/Y<1, which is near to marble lithology. Also, about vein deposit, the sample is ore making in alkaline conditions, and other samples show acidic conditions. To evaluate the segregation coefficient between REEs, different ratios of REEs including (La/Yb) n ', (La/Sm) n, and (Gd/Yb) n are used. The values of these ratios range from (0.42 to 50.56) for (La/Yb) n; and from (0.25 to 80.125) for (La/Sm) n’; (from 0.006 to 48.8) for (Gd/Yb) n. The highest segregation was between LREEs and HREEs (more than 125) and the least segregation was between MREEs and HREEs during the Skarn process.

Re-Os Geochronology and Sulfur Isotopes of the Lyangar W-Mo Deposit: Implications for Permian Tectonic Setting in South Tianshan Orogen, Uzbekistan

The Lyangar W-Mo skarn deposit is located in the Nuratau area (western Uzbekistan), South Tianshan Orogen. The skarn system is distributed along the contact zone between the Aktau granitoid and the upper Paleozoic sedimentary rocks. Six molybdenite samples from the Lyangar deposit yielded a Middle Permian Re-Os isochron age of 268.0 ± 12 Ma (MSWD = 0.43) and a weighted mean age of 263.8 ± 1.5 Ma (MSWD = 0.22). Molybdenites have low Re contents (12.49 to 16.65 ppm), indicative of a continental crust-dominated source. The molybdenite δ34S values fall inside a narrow range (1.0 to 3.8‰; average 2.3‰), implying that the ore metals were likely derived from the granite intrusion. We concluded that the Lyangar W-Mo deposit was formed in a post-collisional setting caused by continental collision between the Tarim and Kazakhstan cratons.