Mineralogical Characteristics and Short-wave Infrared Spectra of Chlorite as Indicators of Hydrothermal Centers: A Case Study of the Giant Porphyry Copper–Molybdenum Deposit at Qulong, Tibet,Acta Geologica Sinica-English Edition

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Mineralogical Characteristics and Short-wave Infrared Spectra of Chlorite as Indicators of Hydrothermal Centers: A Case Study of the Giant Porphyry Copper–Molybdenum Deposit at Qulong, Tibet
Acta Geologica Sinica-English Edition ( IF 3.3 ) Pub Date : 2021-09-20 , DOI: 10.1111/1755-6724.14809
Tang Nan ₁ , Qin Zhipeng ₁ , Li Yubin _{1,

2,

3} , Duo Ji ₄ , Ran Fengqin ₁ , Dai Jingjing ₅

Affiliation

The Qulong deposit in Tibet is one of the largest porphyry copper–molybdenum deposits in China. We used short-wave infrared (SWIR) spectroscopy to examine the spectral characteristics of the extensively developed chlorite in this deposit. X-ray diffraction and electron microprobe analyses were used for phase identification and to obtain the chemical composition, ion substitution relationships, and formation environment of the chlorite. SWIR spectral parameters were applied to detect the hydrothermal centers. The results indicate that the wavelength at the absorption peak of Qulong chlorite Fe-OH (Pos2250) varies between 2240 and 2268.4 nm; the chlorite substitution relationships are dominated by Mg-Fe substitution at the octahedral sites together with Al^IV-Si substitution at the tetrahedral sites; the chlorite formation temperatures range within the medium-low temperature hydrothermal alteration range from 164 to 281 °C, with an average value of 264 °C; the wavelength of the chlorite peak position for Fe-OH (2250 nm) absorption and its chemical composition are positively correlated with Al^VI, Fe+Al^VI, Fe/(Fe+Mg), Fe, and Fe+Al^IV but negatively correlated with Mg and Mg/(Fe+Mg); and the wavelength associated with the chlorite Fe-OH (2250 nm) absorption peak position is positively correlated with the temperature at which the chlorite formed. These correlations indicate that more Fe and Al^VI ions and fewer Mg ions at the octahedral sites of chlorite lead to a longer the wavelength of the chlorite Fe-OH (2250 nm) absorption peak position and a higher chlorite formation temperature. The wavelength of the Qulong chlorite Fe-OH (2250 nm) absorption peak position (> 2252 nm) can thus serve as an exploration indicator to guide the detection of hydrothermal centers in porphyry copper deposits. The results of the study indicate that the mineralogical and SWIR spectral characteristics of chlorite are significant indicators for locating hydrothermal centers within porphyry deposits.

更新日期：2021-09-20

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