Genesis of the Xiaotongchang basalt-hosted copper deposit in the Jinping area, SW China: Constraints from geochronology, fluid inclusion and geochemistry
Graphical abstract
Introduction
Basalt-hosted copper deposits, known as volcanic redbed copper deposits, were first proposed by Kirkham and were mainly divided into two types: sulfide copper deposits and native copper deposits (Kirkham et al., 1984, Kirkham, 1993). Distributing all over the world, the basalt-hosted copper deposits are mostly associated with mantle plume, such as the Keweenaw-type copper deposits in America, basalt-hosted copper deposits in SW China (Kirkham et al., 1984, Zhu et al., 2002b, Zhu, 2003, Symons and Kawasaki, 2019) and the Brazil native copper hydrothermal deposit in the Paraná volcanic province (Baggio et al., 2017). Previous researches suggested that there are some basalt copper deposits that have no relation with magmatic activity of mantle plume, such as the Dochileh stratiform copper deposit in the Sabzevar Zone of northeastern Iran (Ebrahimi et al., 2019), the native copper deposits with metallogenic age concentrating in 310–270 Ma and sulfide copper deposit with an age of 353 Ma in the Jueluotage belt in East Tianshan area, Xinjiang Province, NW China, which formed in the post-collisional extensional environment (Yuan et al., 2010, Zhang et al., 2013, Wang et al., 2018a). The basalt-hosted copper deposits in the Emeishan Large Igneous Province (ELIP), SW China, were affected both by mantle plume and tectono-magmatic activity, and thus research on the genesis of basalt-hosted copper deposit is important to understand their metallogenic condition.
According to metallogenic factors and geological characteristics, previous studies divided Emeishan basalt-hosted copper deposits into four types including volcanic eruptive type; volcanosedimentary type; tectonic hydrothermal type and fracture-controlled vein-type (Zhao et al., 2005, Zhu, 2011, Zhao and Xu, 2018, Ding, 2019). Many studies have focused on the genesis of basalt-hosted copper deposits, but the relationship between the Emeishan flood basalt and basalt-hosted copper deposit remains controversial (Li et al., 2004, Zhang et al., 2004, Zhao et al., 2005, Wang et al., 2011b). Some scholars suggested that the Emeishan flood basalt was an important metal source for copper deposits (He et al., 2003, Zhang et al., 2006, Hou et al., 2007, Fu et al., 2012, Cai et al., 2013, Xu et al., 2014). Xu et al. (2014) have presented a model to interpret the lack of temporal association between the basalt-hosted copper deposits and the Emeishan basalt. They considered the Emeishan basalt should be the main source of the ore-forming metals and fluids, and basalts would eventually release metal-bearing fluid after several tens of millions of years. However, the existing data, such as metallogenic ages, which are concentrated in 235–228 Ma and 187–162 Ma (Zhu et al., 2005) and metallogenic fluids of native copper deposits that were characterized by mixing of meteoric water, hot brine of the basin and magmatic water (Li, 2009) are hardly to provide direct evidence for the relationship between the Emeishan basalt and the basalt-hosted copper deposits.
The Jinping basalt belongs to the Emeishan flood basalt (Nian et al., 2006, Zhang, 2006, Wang et al., 2007), and the left slip movement of the Ailaoshan-Red River fault in Cenozoic brought it to the present position (Tang, 2010) (Fig. 1a). High copper content of basalt led it to the main copper-bearing formation in the area, and formed many basalt-hosted copper deposits, such as the Yanpo, Xiaotongchang and Longgu deposits (Fig. 1b). The Xiaotongchang basalt-hosted copper deposit in the Jinping area, Yunnan Province, is located in the junction of the Qinghai-Tibet-Yunnan plate and Ailaoshan metamorphic terrane (Nian et al., 2006, Zhang, 2006, Wang et al., 2007, Shen et al., 2010, Shellnutt, 2014, Zhang et al., 2019) (Fig. 1a). Shen et al. (2019) proposed that the early-stage (256 ± 9.4 Ma) ore body in the Xiaotongchang deposit is syngenetic hydrothermal mineralization related to the eruption of Emeishan flood basalt, and the late-stage (240–231 Ma) ore body is magmatic hydrothermal mineralization related to the Late Triassic rhyolite porphyry. Li et al. (2019b) obtained metallogenic age of 230.6 ± 1.1 Ma in the Xiaotongchang deposit by chalcopyrite Re-Os isotopic analysis, which indicated a close relationship with the late collisional process in the Ailaoshan orogenic belt. The previous studies have suggested that the Xiaotongchang deposit was affected by Emeishan mantle plume and later magmatic hydrothermal fluids based on the geological characteristics and metallogenic age of the deposit, but the main-stage mineralization age is not accurate and the characteristic of ore-forming fluids is unclear.
In this study, we analyze the geochemical characteristics of basalt and minerals in ores to trace the metal source and tectonic setting of the deposit. H-O isotopes and fluid inclusions of quartzs were analyzed to elaborate the characteristics of ore-forming fluid. The zircon U-Pb and chalcopyrite Re-Os isotopic dating of copper ore were taken to constrain the metallogenic age. Then, the genetic model of the Xiaotongchang basalt-hosted copper deposit is proposed. Our study will provide direct evidence for association between the Emeishan flood basalt and basalt-hosted copper deposit, and provide directions for further geological exploration in the ELIP.
Section snippets
Regional geology
The Jinping area is located in the southwestern margin of Ailaoshan orogenic belt, which formed by convergence of the Yangtze massif and Simao-Indosinian massif (Fig. 1a). The exposed faults in the area are mainly NW-trending Red River fault, Ailaoshan fault and Tengtiaohe fault. The regional strata are exposed from Lower Silurian to Quaternary. The Lower Silurian, Tertiary and Quaternary are dominated by clastic rocks, and the Middle-Upper Permian is dominated by basalts, whereas others are
Analytical methods
In order to understand the characteristics of basalts in different eruptive cycles in the Xiaotongchang deposit, ten basalt samples were collected from LD-3, LD-7, LD-8 and LD-10 tunnels, which were located from the first cycle to the fourth cycle. Minerals such as zircon, chalcopyrite, pyrite, quartz and calcite were handpicked from copper ores under a binocular microscope. The purity of each single mineral separate was better than 99%. We cleaned all mineral separates in an ultrasonic bath
Major and trace elements
Basalt samples were collected from the first cycle (JM-154, JM-157), the second cycle (JM-159, JM-161, JM-162, JM-165), the third cycle (JM-175, JM-176, JM-179) and the fourth cycle (JM-169). Most of the samples fell in the alkaline basalt region and four samples (JM-159, JM-175, JM-176, JM-179) fell in the subalkaline basalt region on the Silica-Alkali diagram (Fig. 7). The values of (K2O + Na2O)/(SiO2-39) range from 0.02 to 0.71 (Table 1), suggesting that the Xiaotongchang basalts belong to
Assimilation and contamination
According to analysis of the covariant relationship between the ratios of elements, which have similar total distribution coefficients and are sensitive to assimilation and contamination (such as Ce/Pb, Th/Yb, Nb/Ta, Ta/Yb, K2O/P2O5, Ti/Yb, Zr/Nb, etc.), assimilation-contamination can be accurately indicated and the degree of contamination can be determined (Baker et al., 1997, Macdonald et al., 2001). The diagrams suggest that the Xiaotongchang basalts experienced some degree of assimilation
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We are grateful to Mu Liu for help with major and trace elements testing, to Yi Zhang for help with fluid inclusion analysis, and to Professor Ryan Mathur for Re-Os isotopic dating. This study was financially supported by the National Natural Science Foundation of China (Grant No. 41502064 and 41602110), the Project of Shandong Province Higher Educational Science and Technology Program (Grant No. J18KA213), the Scientific Research Foundation of Shandong University of Science and Technology for
References (141)
- et al.
A new model for the Indochina and South China collision during the Late Permian to the Middle Triassic
Tectonophysics
(2009) - et al.
Alteration effects of volcanic ash in seawater: Anomalous Y/Ho ratios in coastal waters of the Central Mediterranean sea
Geochim. Cosmochim. Acta
(2007) - et al.
Re–Os isochron ages for arsenopyrite from Carlin-like gold deposits in the Yunnan–Guizhou–Guangxi “golden triangle”, southwestern China
Ore Geol. Rev.
(2015) Variation of mineralizing fluids and fractionation of REE during the emplacement of the vein-type fluorite deposit at Bozijan, Markazi Province, Iran
J. Geochem. Explor.
(2012)- et al.
Triassic tectonics of the Ailaoshan Belt (SW China): Early Triassic collision between the South China and Indochina Blocks, and Middle Triassic intracontinental shearing
Tectonophysics
(2016) - et al.
Geochronology and geochemistry of the ‘green-bean rock’ (GBR, a potassium-rich felsic tuff) in the western margin of the Yangtze platform, SW China: Significance for the Olenekian-Anisian boundary and the Paleo-Tethys tectonics
Lithos
(2021) - et al.
Re-Os, Sm-Nd, U-Pb, and stepwise lead leaching isotope systematics in shear-zone hosted gold mineralization: genetic tracing and age constraints of crustal hydrothermal activity
Geochim. Cosmochim. Acta
(1998) - et al.
Sedimentary evidence for a rapid, kilometer-scale crustal doming prior to the eruption of the Emeishan flood basalts, Earth Planet
Sci. Lett.
(2003) - et al.
Organic geochemical study of mineralization in the Keweenawan Nonesuch Formation at White Pine, Michigan
Adv. Org. Geochem.
(1990) - et al.
Nb and Pb in oceanic basalts: new constraints on mantle evolution
Earth Planet. Sci. Lett.
(1986)