The controlling role of magmatic factors on the differential mineralization in the Tongling ore district, eastern China: Evidence from the mineralogy of amphibole and plagioclase

doi:10.13745/j.esf.sf.2023.12.60

Abstract

Abstract:

The Dongguashan Cu (Au) deposit and the Xinqiao S-Fe-Cu-Au deposit are two large skarn-type deposits in the Tongling Ore District. These deposits share a similar metallogenic geological background and are located in the same stratigraphic horizon. However, they exhibit distinct differences in mineral assemblages with the Dongguashan deposit being dominated by chalcopyrite and pyrrhotite, while the Xinqiao deposit is characterized by pyrite and magnetite dominance. The factors influencing these contrasting mineral assemblages remain unclear. To address this scientific question, this study focuses on amphibole and plagioclase in the ore-forming rock masses of both deposits to investigate the magmatic influences on their differential mineralization. Petrographic analysis, EPMA major element analysis, and LA-ICP-MS trace element analysis were conducted on amphibole and plagioclase from the Qingshanjiao quartz monzodiorite of the Dongguashan deposit and the Jitou quartz diorite of the Xinqiao deposit. The results reveal that most amphiboles in the Qingshanjiao rock mass belong to the magnesium amphibole series, whereas those in the Jitou rock mass belong to both the magnesium amphibole and amphibole series. The crystallization pressure, crystallization temperature, crystallization depth, oxygen fugacity and water content of amphibole in the Qingshanjiao and Jitou intrusions are 41-306 MPa and 23-225 MPa, 691-916 ℃ and 634-918 ℃, 1.6-11.6 km and 0.9-8.5 km, ΔNNO=0-2.3 and ΔNNO=-0.4-2.4, 3.7%-5.5% and 3.1%-5.4%, respectively. The amphiboles in both intrusions are predominantly of crustal origin, with some showing characteristics of crust-mantle mixing. Plagioclase in both rock masses is predominantly feldspar. Based on the structure and composition profile of plagioclase, it is suggested that the crystal groups in the Qingshanjiao and Jitou rock masses originate from five and four different magma subsystems, respectively, and have undergone mafic magma injection and mixing. The study proposes that variations in oxygen fugacity and element content in mafic magmas play a key role in controlling the differential mineralization observed in the Dongguashan and Xinqiao deposits.

Key words: amphibole, plagioclase, genetic mineralogy, skarn-type deposit, Tongling ore district

CLC Number:

CHEN Ke, SHAO Yongjun, LIU Zhongfa, ZHANG Junke, LI Yongshun, CHEN Yuying. The controlling role of magmatic factors on the differential mineralization in the Tongling ore district, eastern China: Evidence from the mineralogy of amphibole and plagioclase[J]. Earth Science Frontiers, 2024, 31(3): 199-217.

Figures/Tables 17

Fig.1 Sketch geological map of magmatic rocks and deposits in the MLYB. Modified after [8].

Fig.2 Geological map of the Tongling ore district. Modified after [8].

Fig.3 (a) Geological map of the Shizishan ore field; (b) Typical cross-section of the Dongguashan deposit. a modified after [27]; b modified after [32].

Fig.4 (a) Geological map of the Xinqiao ore field; (b) Typical cross-section of the Xinqiao deposit. a modified after [23]; b modified after [31].

Fig.5 Hand specimens and microscopic photos of Qingshanjiao and Jitou quartz (oligoclase) diorites

Fig.6 Classification diagram of amphibole in Qingshanjiao and Jitou quartz (oligoclase) diorites. Adapted from [38].

Fig.7 Classification diagram of plagioclase in Qingshanjiao and Jitou quartz (oligoclase) diorites

Fig.8 Backscattered electron images (left) and the composition profiles (right) of the representative plagioclase grains in the Qingshanjiao pluton

Fig.9 Trace element composition profile of plagioclase in the Qingshanjiao rock body

Fig.10 Backscattered electron images (left) and the composition profiles (right) of the representative plagioclase grains in the Jitou pluton

Fig.11 Trace element composition profiles of representative plagioclase grains in the Jitou pluton

Fig.12 BSE images(left) and the composition profiles (right) of the representative amphibole grains in the Qingshanjiao pluton

Fig.13 BSE images (left) and the composition profiles (right) of the representative amphibole grains in the Jitou pluton

Fig.14 p-T(a),$\lg f_{\mathrm{O}_{2}}$ -T(b),H2Omelt-p(c) and ΔNNO-h(d) plots for amphibole from the Qingshanjiao and Jitou quartz (monzo) diorite

Fig.15 Si-(Si+Ti+Al)(a),Mg-(Mg+Fe2+)(b),TiO2-Al2O3(c),(Na+K)-IVAl(d),AlT-Si(e) and Ca-(Fe2++Fe3+)-Mg(f) plots for amphibole from the Qingshanjiao and Jitou quartz (monzo) diorite

Fig.16 The schematic diagram showing a possible magmatic system for the Qingshanjiao and Jitou quartz (monzo) diorites

Fig.17 Ba-Sr(a) and Fe-Mg(b) plots for plagioclase from the Qingshanjiao and Jitou quartz (monzo) diorites

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