The field radiometric and laboratory measurements were performed at the Sin Quyen copper deposit in North Vietnam. The field gamma-ray spectrometry indicated the concentration of uranium ranging from 5.5 to 87 ppm, thorium from 5.6 to 33.2 ppm, and potassium from 0.3 to 4.7%. The measured dose rates ranged from 115 to 582 nGy/h, the highest doses being at the copper ore. Concentrations in the solid samples were in the range of 20-1700 Bq/kg for uranium, 20-92.7 Bq/kg for thorium, and 7-1345 Bq/kg for potassium. The calculated doses were from 22 to 896 nGy/h; both measured and calculated dose rates are mostly related to uranium. Concentrations of radium in water samples were below 0.17 Bq/L. Uranium in water samples was significantly higher than the hydrogeological background; the maximum of 13 Bq/L was at the waste zone pool, but neither radium nor uranium were present in tap water. Radon concentration in the dwelling air was from 42 to 278 Bq/m 3 for 222 Rn and from 8 to 193 Bq/m 3 for 220 Rn. The estimated committed dose rates D.C. NGUYEN et al. 2306 were principally related to 222 Rn concentration and ranged from 1.1 to 8.1 mSv/y.
As so ci ate Ed i tor: Jacek Szczepañski Mag ne tite, py rite, pyrrhotite, chal co py rite and sphalerite are the ma jor min er als iden ti fied in the de posit, while il men ite, marcasite, ten nan tite, cubanite, ar seno py rite, ga lena, al la nite, chevkinite, ap a tite, Bi-na tive, bis muthi nite, electrum, na tive gold, and tellurides are the mi nor ones in the Iron Ox ide Cop per Gold (IOCG) Sin Quyen de posit. The REEs are hosted mostly by al la nite, and the mi nor min er als by chevkinite, monazite, ap a tite and uraninite. Based on chem i cal anal y ses and Raman spec tros copy, two va ri et ies of al la nite have been doc u mented: (1) with lower to tal REE con tents of 13-19 wt.%, and (2) with higher con tents of 20-23 wt.%. Uraninite from cop per-iron mas sive ores is inhomogeneous in both op ti cal prop er ties and chem i cal com po si tion. The con cen tra tions of ura nium and to tal rare earth el e ment ox ides (REOs) in the paragenetically ear lier uraninite are 84.55-85.96% and 1.9-8.0% on av er age, re spec tively, whereas in paragenetically later uraninite, the U and SREE 2 O 3 con cen tra tions are 96.2-96.7% and 1.3-2.7% on av er age re spec tively. The tho rium con cen tra tion in both the early and late uraninites is very low (0.21-0.22% and 0.2 % on av er age). These are the high est REE con cen tra tions as compared with the known con cen tra tions of these el e ments in uraninite. Elec tron microprobe "chem i cal" dat ing of the uraninite yielded an age of 500 ±33 Ma (n = 35) for the paragenetically early uraninite, and an age of 73 ±15 Ma (n = 6) for the paragenetically later ones. The min er als of the older age, which is in ter preted as the pri mary ore min er al iza tion stage, cor respond in age with a range of de pos its along the East Gond wana mar gin. The mea sured d 34 S of sul phide min er als from-2.78 to +8.65‰ sug gests hy dro ther mal or i gin of fluid that was re spon si ble for trans por ta tion and crys tal li za tion.
Allanite minerals are the principal host of REEs in the Sin Quyen, Iron Oxide Copper Gold (IOCG) type deposit. The geochemical characteristics of these minerals are discussed in this work. The studied allanites have an unstable concentration of all major elements, such as REE (14-27 wt%), Ca (9-16 wt%), Al (8-19 wt%), Si (26-34 wt%) and Fe (12-21 wt%). Two different varieties of these minerals are documented, the older with higher REE concentrations ranging from 20 to 27 wt%, and younger with lower total REE concentration ranging from 14 to 19 wt%, which occur as a rim surrounding the older. Differences between the two groups of allanites are documented by Raman spectra and optical properties. The WDS chemical composition indicate that the allanites belong to the Ce-La-ferriallanite family, with low ƩHREE with an average of 0.21 wt.%. This work also supports the estimated timing of the deposit development focusing on detailed petrological study, and documented chemical composition of allanites confirmed by simplified statistical analysis. Temperature 355ºC which was calculated using value of δ34S isotopes is interpreted as a temperature of the second crystallization stage of allanite group. The pressure of crystallization solution was calculated and is ranging from 0.98 to 5.88 MPa.
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