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The Characteristics of Garnet in the Hongniu Skarn Copper Deposit, Western Yunnan, China
Author(s) -
GAO Xue,
YANG Liqiang,
DENG Jun,
MENG Jianyin,
YANG Chunhai,
LI Jianxin
Publication year - 2014
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.12374_11
Subject(s) - beijing , china , skarn , chinese academy of sciences , geology , mining engineering , mineral resource classification , geochemistry , library science , geography , archaeology , computer science , seismology , fluid inclusions , hydrothermal circulation
copper deposit situated in the southern part of Yidun island arc, southeast Tibet (Li et al., 2010; Deng et al., 2013; Yang et al., 2011). Distinctly different from the typical skarn deposits, its skarn and hornfels usually arranged alternately, consisting with the attitude of stratum. Skarn is not in direct contact with the intrusive rocks but direct contact with the marble (Meng et al., 2013). There are coarse garnet and wollastonite visible in the marble, while, there also have marble xenoliths in the skarn. Therefore, the deposit is the product of concealed intrusive rocks, belonging to the far skarn type (Li et al., 2010). Garnet is the most important skarn mineral in the Hongniu deposit, and it is therefore significant to study characteristics of garnet due to its wide distribution, various colors and strong mineralization. Through systematic field work and the made-up of drills holes, we collects some fresh garnet skarn and a small amount of skarnized marble to make thin sections, carrying out detailed microscopic identification, to induce the characteristics of garnet and analyze its chemical composition by electron probe. Garnet has two obvious stage. Early garnets (GrtI) are widely distributed, brown-red to brown, hypidiomorphicidiomorphic medium grained texture, with anomalous optical characteristics on the cross-polarized light, and their particle size is generally between 0.2-4mm, developing zonation patterns (Fig.1). Changes in the content scope of the SiO2 is 35.85%-37.58%, CaO is 33.34%-34.94%, Al2O3 is 3.64%-13.69%, FeO is 11.90%24.18%, MgO is 0.00%-0.08%, and there is a negative correlation between the content of FeO and Al2O3, while an overall positive correlation between the content of SiO2 and CaO. The end members of garnet are mainly andradite (32.96-82.36), followed by grossular (16.59-64.84), and there are a small number of pyrope, belonging to andradite-grossular series (And33-82Gro1765Spe+Pyr+Alm0.48-3.53). The garnets of later stage (GrtII) are brownish to light red (Fig.1), usually veinlike distributed in skarnized hornfels and marble, also can be seen in some kinds of skarn. Changes in the content scope of the SiO2 is 35.06%-36.27%, CaO is 33.07%-33.97%, Al2O3 is 0.04%-1.05%, FeO is 27.38%-28.18%, MgO is 0.00%-0.04%, the composition of end members belong to andradite. Changes in contents of major elements in zoned garnet shows a certain regularity, from the core to the rim, the content of FeO increased, the content of Al2O3 decreased, the content of andradite increased, the content of grossular decreased, reflecting the diagenetic environment was acidic and reduced with low oxygen fugacity when the garnet began to form (Jamtveit et al., 1993). During the process of the crystal formation, the oxygen fugacity increased, and the ore-forming solution shifted from acidic GAO Xue, YANG Liqiang, DENG Jun, MENG Jianyin, YANG Chunhai and LI Jianxin, 2014. The Characteristics of Garnet in the Hongniu Skarn Copper Deposit, Western Yunnan, China. Acta Geologica Sinica (English Edition), 88(supp. 2): 515-516.