Sao Pedro das Aguias skarn: A W-(Sn) deposit from the Douro Scheelite Belt, Northern Portugal

• Type: Article in International Scientific Journal
• Date: 2024

Authors

Ramos, V (Author) Other; Noronha, F (Author) FCUP; Seltmann, R (Author) Other; Dolgopolova, A (Author) Other; Guedes, A (Author) FCUP; Andersen, J (Author) Other; Spruzeniece, L (Author) Other; Simons, B (Author) Other; Rollinson, G (Author) Other; Pickles, J (Author) Other; Armstrong, R (Author) Other; Stanley, C (Author) Other; Reimer, W (Author) Other

Journal

Title: Ore Geology Reviews

Vol. 175

ISSN: 0169-1368

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 0 Citations

Scopus - 0 Citations

Other information

Authenticus ID: P-017-M6S

DOI: 10.1016/j.oregeorev.2024.106348

Abstract (EN): The Sao Pedro das Aguias skarn deposit is one of the most significant tungsten deposits in the Douro Scheelite Belt, located in Northern Portugal. It is situated at the contact between the Bateiras Formation of the SchistGreywacke Complex and contains scheelite as the primary tungsten mineral, along with some minor tin minerals. A recent evaluation suggests indicated resources of 1,495 kt with 0.55 wt% WO3 and inferred mineral resources of 1,230 kt with 0.59 wt% WO3. The deposit hosts scheelite (CaWO4) as the major tungsten mineral, along with minor tin minerals. Two distinct skarn layers are identified at the deposit, differentiated by their stratigraphic positions: an Upper Skarn and a Lower Skarn, separated by approximately a 50-meter-thick sequence of schists. Based on its structural, mineralogical, and geochemical characteristics, three main types of skarns can be distinguished: L Type, characterized by pink and green bands, fine to medium-grained with minor scheelite (0.5-0.6 vol%); M Type, banded, medium to coarse-grained, with more abundant scheelite (0.8-3.6 vol%); and F Type, fine-grained, scarcely banded to massive, with scheelite (1.5 vol%) and abundant tin minerals (3.1 vol%), primarily malayaite. A typical characteristic of this W-(Sn) skarn is its high content in W (from 2,260 to over 10,000 ppm), Sn (from 405 to 7,770 ppm), and F (from 6,820 to over 20,000 ppm). These skarns can be distinguished by their rare earth element (REE) contents, with higher values (average TREE = 130 ppm) in the L Type skarn and lower values (average TREE = 66 ppm) in the M Type skarn. The composition of scheelite grains can vary within the same sample, exhibiting different chemical compositions and REE patterns, suggesting a complex formation process. In the richest M Type skarn, scheelite is characterized by REE depletion. Its Mo content is always low: less than 123 ppm in the L Type and less than 26 ppm in the M Type. These scheelite compositions can be regarded as characteristic of reduced skarns. This study shows that scheelite records the history of the hydrothermal system related to the formation of Sao Pedro das Aguias reduced skarns. Scheelite deposition is triggered by the crystallisation of F-rich minerals during skarn formation, which caused F and REE depletion in the fluid and consequent saturation in W.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 22