Mineralogy, Fluid Inclusions, and Oxygen Isotope Geochemistry Signature of Wolframite to Scheelite and Fe,Mn Chlorite Veins from the W, (Cu,Mo) Ore Deposit of Borralha, Portugal

• Type: Article in International Scientific Journal
• Date: 2022

Authors

Bobos, I (Author) FCUP; de Sa, CM (Author) Other; Noronha, F (Author) FCUP

Journal

Title: Minerals

Vol. 195

Final page: 24

Publisher: MDPI

Indexing

ISI Web of Knowledge - 0 Citations

Scopus - 0 Citations

Other information

Authenticus ID: P-00V-WSS

DOI: 10.3390/min12010024

Abstract (EN): Scheelitization of Mn-bearing wolframite, scheelite, quartz, and Fe,Mn-chlorite veins was identified in the W, (Cu,Mo) ore deposits of Borralha, by optical microscopy, electron-microprobe analysis, and stable isotope geochemistry. Fluid inclusions derived scheelite crystallization temperature was compared with the oxygen isotope temperature estimated. Scheelite was formed mainly during stage I from a low salinity aqueous-carbonic fluid dominated by CO2, where the homogenization temperature (T-h) decreased from 380 degrees C to 200 degrees C (average of 284 degrees C). As temperature decreased further, the aqueous-carbonic fluid became dominated by CH4 (Stage II; (average T-h = 262 degrees C)). The final stage III corresponds to lower temperature mineralizing aqueous fluid (average T-h = 218 degrees C). In addition, salinity gradually decreased from 4.8 wt.% to 1.12 wt.%. The delta O-18(Fluid) values calculated for quartz-water and wolframite-water fractionation fall within the calculated magmatic water range. The increment (quartz-scheelite) fractionation occurred at about 350-400 degrees C. The increment (chlorite-water) fractionation factor calculated is about +0.05 parts per thousand for 330 degrees C, dropping to -0.68 parts per thousand and -1.26 parts per thousand at 380 degrees C and 450 degrees C, respectively. Estimated crystallizing temperatures based on semi-empirical chlorite geothermometers range from 373 degrees C to 458 degrees C and 435 degrees C to 519 degrees C. A narrower temperature range of 375 degrees C to 410 degrees C was estimated for Fe,Mn-chlorite crystallization.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 25