21 research outputs found
Conditions for Early Cretaceous emerald formation at Dyakou, China: fluid inclusion, Ar-Ar, and stable isotope studies
The Dyakou emerald occurrence is located in Malipo County in the province of Yunnan, southern China.
The occurrence lies in the northern part of the Laojunshan-Song Chay metamorphic core complex, which is
exposed in an area of approximately 2,000 km2 and extends across the border between China and Vietnam.
Emerald mineralization is hosted by pegmatite and associated quartz veins that intrude deformed Proterozoic
biotite-muscovite granofels and schist. Hydrogen and oxygen isotope results from the emerald channel waters
and emerald, respectively, are consistent with an igneous fluid source. The δ18O fractionation between emerald
and quartz yields vein temperatures of 365° to 420°C. Fluid inclusions indicate that the emerald precipitated
from saline brines ranging from almost pure water to 10.5 mass percent NaCl equiv. Fluid inclusion isochores
intersected with δ18O data yield pressures changing along the geothermal gradient from 1,500 to 3,300
bars. Ar-Ar geochronology of biotite and muscovite from the emerald veins yields consistent ages of 124 ± 1
Ma. These constraints combined with field observations indicate that the Dyakou emerald deposit is consistent
with the igneous-related model for emerald formation