El yacimiento de Zn-Pb de Castellanos (Cuba): un depósito sedimentario-exhalativo finijurásico-cretácico

The Castellanos Zn-Pb deposit (Cuba): a late Jurassic-Cretaceous sedimentary-exhalative deposit

David Gómez-Vivo¹, Fernando Gervilla^2,3,*, Antonio Azor⁴, Rebeca Hernández-Díaz¹ , Ruben Piña⁵, Carmen María Álvarez²

¹ Departamento de Geología, Universidad de Pinar del Río Hermanos Saiz Montes de Oca, Pinar del Río, Cuba.

² Departamento de Mineralogía y Petrología, Facultad de Ciencias, Universidad de Granada, avd. Fuentenueva s/n, 18071, Granada, España.

³ Instituto Andaluz de Ciencias de la Tierra (UGR-CSIC), avd. de las Palmeras 4, 18100 Armilla, Granada, España.

⁴ Departamento de Geodinámica, Facultad de Ciencias, Universidad de Granada, avd. Fuentenueva s/n, 18071, Granada, España.

⁵ Departamento de Mineralogía y Petrología, Facultad de Geología, Universidad Complutense de Madrid, José Antonio Nováis 12, Ciudad Universitaria, 28040, Madrid, España.

* Autor para correspondencia: (F. Gervilla) This email address is being protected from spambots. You need JavaScript enabled to view it.

How to cite this article:

Gómez-Vivo, D., Gervilla, F., Azor, A., Hernández-Díaz, R., Piña, R., Álvarez, C.M., 2023, El yacimiento de Zn-Pb de Castellanos (Cuba): un depósito sedimentario-exhalativo finijurásico-cretácico: Boletín de la Sociedad Geológica Mexicana, 75 (1), A161122. http://dx.doi.org/10.18268/BSGM2023v75n1a161122

Manuscrito recibido: 12 de Mayo de 2022; Manuscrito corregido: 10 de Octubre de 2022; Manuscrito aceptado: 4 de Noviembre de 2022.

ABSTRACT

The Castellanos Zn-Pb deposit in northwest Cuba is hosted by black shales intercalated in the upper part of a thick siliciclastic sequence (>4km) mainly made up of sandstones and siltstones of Lower to Middle Jurassic age (San Cayetano Formation). The ore deposit is tabular to wedge-shaped and stratiform, oriented NE-SW conformably with the stratification of the host black shales and appears splitted into two blocks (the Farallones block to the NE and the Susana block to the SW) by a N120ºE-oriented fault zone; a similarly oriented fault zone marks the NE contact of the Farallones block. This block overlies a stockwork zone made up of <10cm-thick, pyrite-chalcopyrite-quartz veins striking N120ºE too. The orebody consists of pyrite, sphalerite and galena, with carbonates (mainly dolomite-ankerite and calcite), quartz, and barite, as well as minor percentages of sericite, partly altered biotite and cryptocrystalline apatite. The internal structure is zoned and consist of a discontinuous, lower pyrite-rich level overlayed by a heterogeneous ore level with variable sulfide+carbonate (locally with quartz) modal proportions, as well as variable amounts of sphalerite+galena relative to pyrite. The upper level shows a broad banded texture defined by alternating pyrite-rich, sphalerite+galena and dolomite-ankerite (±sericite, partly altered biotite and cryptocrystalline apatite) bands, which becomes better defined towards the SW part of the orebody. Modal proportions of quartz and to a lesser extent barite increase too from NE to SW and from bottom to top, especially within the Susana block. An additional NE-SW trend is observed in the chemical composition of sphalerite, whose Fe content decreases southwestwards; this Fe-poor sphalerite coexists with a second generation of sphalerite containing even lower Fe (<1wt.%). Different events of fracturing and brecciation affected the sulfide ore near the N120ºE oriented fault zones, which promoted precipitation and remobilization of several generations of calcite, barite, quartz and galena. The late events also allowed precipitation of chalcopyrite filling fractures and interstitial spaces among fragments of the previous sulfide ore. The proposed genetic interpretation of the Castellanos orebody is based on the repeated (multiphase) precipitation of sulfides+carbonates due to the interaction between ore-forming brines migrating upwards through the stockwork fractures and organic matter-rich sediments deposited in an anoxic sub-basin developed in the major passive-margin basin where the sandstones and siltstones of the San Cayetano Formation accumulated. The ore-forming brines were oxidizing, saturated in sulfate, and generated in the evaporite-bearing carbonate platform developed at the margins of the passive-margin basin from Upper Jurassic to Lower Cretaceous times. The infiltration of these brines through the thick siliciclastic sequence gave rise to a significant increase in temperature (up to 100-200ºC), thus promoting dissolution and remobilization of the Zn and Pb quantities necessary to form the main sulfide ore. The fracturing and brecciation stages enabled upward migration of reduced fluids equilibrated with black shales intercalated at different levels of the siciliclastic sequence, which, in turn, supplied Au and Ba to the ore. Late fracturing also allowed ascent of deep, hot fluids (~350ºC) capable of precipitating chalcopyrite.

Keywords: Sedimentary-exhalative deposit, Zn-Pb ores, Castellanos Mine, Matahambre-Santa Lucía mining district, Cuba.