Ore-forming fluids associated with granite-hosted gold mineralization
at the Sanshandao deposit,Jiaodong gold province, China
Abstract The Sanshandao gold deposit, with total resources
of more than 60 t of gold, is located in the Jiaodong
gold province, the most important gold province
of China. The deposit is a typical highly fractured and
altered, disseminated gold system, with high-grade,
quartz-sulphide vein/veinlet stockworks that cut Mesozoic
granodiorite. There are four stages of veins that
developed in the following sequence: (1) quartz-K-feldspar-
sericite; (2) quartz-pyrite±arsenopyrite; (3) quartzbase
metal sulfide; and (4) quartz-carbonate. Fluid
inclusions in quartz and calcite in vein/veinlet stockworks
contain C-O-H fluids of three main types. The
first type consists of dilute CO2–H2O fluids coeval with
the early vein stage. Molar volumes of these CO2–H2O
fluid inclusions, ranging from 50–60 cm3/mol, yield
estimated minimum trapping pressures of ‡3 kbar.
Homogenization temperatures, obtained mainly from
CO2–H2O inclusions with lower CO2 concentration,
range from 267–375 C. The second inclusion type, with
a CO2–H2O±CH4 composition, was trapped during
the main mineralizing stages. These fluids may reflect
the CO2–H2O fluids that were modified by fluid/rock
reactions with altered wallrocks. Isochores for CO2-
H2O±CH4 inclusions, with homogenization temperatures
ranging from 204–325 C and molar volumes from
55 to 70 cm3/mol, provide an estimated minimum
trapping pressure of 1.2 kbar. The third inclusion type,
aqueous inclusions, trapped in cross-cutting microfractures
in quartz and randomly in calcite, are post-mineralization,
and have homogenization temperatures
between 143–228 C and salinities from 0.71–7.86 wt%
NaCl equiv. Stable isotope data show that the metamorphic
fluid contribution is minimal and that ore fluids
are of magmatic origin, most likely sourced from 120–
126 Ma mafic to intermediate dikes. This is consistent
with the carbonic nature of the fluid, and the crosscutting
nature of those deposits relative to the host
Mesozoic granitoid.
请点击此处下载
收藏
