SUMMARY
Temperature-pressure conditions of the formation of
gem-bearing marble
at Lục Yên deposit area,
Nguyễn
Thị Minh Thuyết, Ngụy Tuyết Nhung, Nguyễn Ngọc Khôi
Gemstones in Lục Yên area, such as
ruby, sapphire, spinel, etc. have been mined mainly in placer deposits.
However, the main source rocks of gemstones in this area is
calcite and calcite-dolomite marbles of the An Phú Formation which is
characterized by KCMASH chemical system and two mineral parageneses: corundum +
calcite + phlogopite + amphibole and spinel + amphibol + phlogopite +
forsterite + dolomite ± calcite ± clinohumite ± corundum. Based on the
examination of mineral parageneses containing corundum and spinel and the
calculation of parameters of metamorphic reactions of their formation, a
conclusion can be made: the paragenesis containing spinel was formed in the
temperature interval from 593 to 787oC, while the assemblage
comprising corundum was formed at lower temperature interval (from 550 to 693oC).
The pressure of formation for both parageneses is almost the same (about 5.5
kbar).
Ngày
nhận bài: 27/9/2006
Người
biên tập: Phan Trường Thị