Abstract
This paper reports the helium and argon isotope compositions of fluid inclusions hosted in pyrites from Machangqing alkali-porphyry copper deposit in west Yunnan province, China. There is an excellent positive correlation between 3He/36Ar and 40Ar/36Ar, and between 40Ar /4He and 3He/4He in the inclusion-trapped fluids. This indicates that the ore-forming fluid can be considered as a mixture of two endmember components, a modified mantle fluid and crustal fluid. From the noble gas results and combined noble gas and stable isotope behavior, the authors conclude that the former is a high-temperature magmatic fluid differentiated from Machangqing alkali-porphyry and enriched in volatiles such as sulfur and carbon. The crustal fluid is likely a low-temperature meteoric fluid enriched in crustal radiogenic helium but with atmospheric argon isotopic composition. The sulfur and carbon concentrations in the low temperature fluid are probably too low to produce a distinct C or S isotope signature: the mixing between high and low temperature fluids can only be traced using noble gases. In addition, the positive relationship between 3He/4He and δ34S reflects the evolutionary physico-chemical conditions of the mixed fluid.
| Original language | English |
|---|---|
| Pages (from-to) | 55-63 |
| Number of pages | 8 |
| Journal | Chemical Geology |
| Volume | 146 |
| Issue number | 1-2 |
| Publication status | Published - 25 Apr 1998 |