Rb‐Sr and Sm‐Nd Isochron Ages of the Dongmozhazhua and Mohailaheng Pb‐Zn Ore Deposits in the Yushu area, southern Qinghai and Their Geological Implications

Abstract

: Located on the northeast margin of the Qiangtang terrane between the Jinshajiang suture zone and Bangonghu‐Nujiang suture zone, the Dongmozhazhua and Mohailaheng Pb‐Zn deposits in the Yushu area of Qinghai Province are representative Pb‐Zn deposits of the Pb‐Zn‐Cu polymetallic mineralization belt in the northern part of the Nujiang‐Lancangjiang‐Jinshajiang area, which are in the front belt of the Yushu thrust nappe system. The formed environments of these two deposits are different from those of sediment‐hosted base metal deposits elsewhere in the world. The authors hold that they were formed during the Indian‐Asian continental collision and developed within the fold‐thrust belt combined with thrust and strike‐slip‐related Cenozoic basins in the interior of the collisional zone. Studying on the metallogenic epochs of these two deposits is helpful to the understanding of ore‐forming regularity of the regional Pb‐Zn‐Cu mineralization belt and also to the search for new deposits in this region. The age of the Dongmozhazhua deposit has been determined by the Rb‐Sr isochron method for sphalerite residues, whereas the age of the Mohailaheng deposit has been determined by the Rb‐Sr isochron method for sphalerite residues and the Sm‐Nd isochron method for fluorite. The age of the Dongmozhazhua deposit is 35.0±0.0 Ma ((87Sr/86Sr)0=0.708807) for sphalerite residues. The age of the Mohailaheng deposit is 32.2±0.4 Ma ((87Sr/86Sr)0=0.708514) for sphalerite residues and 31.8±0.3 Ma ((143Nd/144Nd)0=0.512362) for fluorite with an average of 32.0 Ma. Together with the regional geological setting during mineralization, a possible tectonic model for metallogeny of the Dongmozhazhua and Mohailaheng Pb‐Zn deposits has been established. These two ages are close to the ages of the Pb‐Zn deposits in the Lanping and Tuotuohe basins, indicating that it is possible that the narrow 1000‐kilometer‐long belt controlled by a thrust nappe system on the eastern and northern margins of the Tibetan plateau could be a giant Pb‐Zn mineralized belt.

The relationship between hydrocarbon accumulation and Mississippi Valley‐type Pb‐Zn mineralization of the Mayuan metallogenic belt, the northern Yangtze block, SW China: Evidence from ore geology and Rb‐Sr isotopic dating

“…Therefore, it is ideal to use the Rb‐Sr isochrone of the hydrothermal paragenetic mineral assemblage to determine the metallogenic age of the hydrothermal deposit (Liu et al ., , ). Based on this principle, scholars obtained reliable Rb‐Sr isochron ages by using the paragenetic mineral assemblage of sphalerite and galena in hydrothermal deposits (Tian et al ., ; Huang et al ., ; Wang et al ., ). Wang et al .…”

“…Tian et al . () studied the Mohailaheng Pb‐Zn deposit in Qinghai province, China, and found that the linear relationship between 87 Rb/ 86 Sr‐ 87 Sr/ 86 Sr obtained from the single mineral sphalerite and paragenetic mineral assemblage of sphalerite and galena is very good. The Rb‐Sr isochron age of sphalerite was t = 32.22 ± 0.36 Ma, initial strontium I Sr = 0.70851380, and mean standard weight deviation (MSWD) = 2.9.…”

“…Therefore, it is ideal to use the Rb-Sr isochrone of the hydrothermal paragenetic mineral assemblage to determine the metallogenic age of the hydrothermal deposit (Liu et al, 1998a(Liu et al, , 1998b. Based on this principle, scholars obtained reliable Rb-Sr isochron ages by using the paragenetic mineral assemblage of sphalerite and galena in hydrothermal deposits (Tian et al, 2009;Huang et al, 2014;Wang et al, 2017). Wang et al (2017) studied the large Uragen Pb-Zn deposit, Xinjiang province, China, and their new Rb-Sr isotopic analyses on paragenetic mineral assemblages of separated sphalerite and galena yielded an isochron age of 55.1 ± 1.6 Ma, coeval to an isochron age of 55.4 ± 2.2 Ma by paragenetic mineral assemblage of galena and calcite Sm-Nd isotopic data, which may represent the age of the Uragen Pb-Zn deposit.…”

Age and Tectonic Setting of Mesothermal Magmatic Hydrothermal Vein‐Type Pb–Zn–(Ag) Mineralization in the Xiaohongshilazi Deposit, Central Jilin Province, Northeast China

“…Hydrothermal deposits form over millions of years, whereas hydrothermal mineral assemblages can form within a few hundred thousand years (Hu et al, 2015; Qiu et al, 2016a, b). Therefore, Rb-Sr isochron dating of mineral assemblages is preferred to that of a single mineral (Luo et al, 1998) as indicated by several previous studies (Li et al, 2004b;Tian et al, 2009;Tao et al, 2010;Zhu et al, 2011;Huang et al, 2014). Rb-Sr dating of hydrothermal minerals requires that the minerals must have been formed simultaneously, and then, the system must have remained closed to Rb and Sr diffusion so that the mineral system has constant 87 Sr/ 86 Sr and variable 87 Rb/ 86 Sr ratios (Li et al, 2002).…”

Fluid inclusions and isotopic characteristics of the Jiawula Pb–Zn–Ag deposit, Inner Mongolia, China

“…It is difficult to eliminate the influence of secondary fluid inclusions in the sulfide samples (Nakai et al, 1990(Nakai et al, , 1993Brannon et al, 1992;Yin et al, 2009) and to extract synthetic fluid inclusions completely with lower total procedural blanks. The ages only constrained by means of Rb−Sr dating of sulfide residues are very precise (Nakai et al, 1990(Nakai et al, , 1993Brannon et al, 1992;Yin et al, 2009;Tian et al, 2014), so we did not analyze the leachate.…”