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GEOREF RECORD

Genesis of vanadium ores in the Otavi mountainland, Namibia

Maria Boni, Rosario Terracciano, Noreen J. Evans, Carsten Laukamp, Jens Schneider and Thilo Bechstaedt
Genesis of vanadium ores in the Otavi mountainland, Namibia
Economic Geology and the Bulletin of the Society of Economic Geologists (May 2007) 102 (3): 441-469

Abstract

Zn-Cu-Pb vanadate ores (descloizite, mottramite, and vanadinite) in the Otavi Mountainland, Namibia, once were considered the greatest vanadium deposits in the world, with resources estimated at several million tons of vanadium ore. The deposits, now mostly exhausted, occurred in collapse breccias and solution cavities related to a karstic network associated with the post-Gondwana land surfaces in carbonate rocks of the Neoproterozoic Otavi Group, which already contained primary sulfide orebodies. Although a supergene, post-Damaran origin has been generally accepted, the timing and genesis of this mineralization style remains controversial. Mottramite and Cu descloizite are particularly abundant around Cu sulfide deposits (Tsumeb type), whereas descloizite occurs in the areas surrounding primary sphalerite-willemite orebodies (Berg Aukas type). The V deposits the Otavi Mountainland represent a special low-temperature, weathering-related, non-sulfide ore type, also fairly widespread in other areas of southern Africa (e.g., Zambia, Angola). Here we describe the geologic setting of the main V deposits and their ore mineralogy, present some comprehensive major and trace element data for the vanadate ore minerals and gangue carbonates, as well as fluid inclusion microthermometry, O, C, Sr, and Pb isotope analyses, and direct (U-Th)/He descloizite thermochronometry. The vanadates are considered to have formed during a late phase in the depositional history of the post-Damaran supergene ores. Calcite and dolomite gangue are paragenetically coeval with the vanadates, occurring with the vein- and breccia-related ores and as cement in the deeper parts of the recent karst infills. The acidic conditions of sulfide alteration, coupled with a low Eh caused by the influence of organic matter, could have been favorable for vanadate precipitation. Geochemical results and isotope data indicate that most vanadate deposits were formed at temperatures of approximately 40 degrees to 50 degrees C by meteoric waters interacting with Neo-proterozoic shales, carbonates, and related primary sulfide ores, which were subjected to multiple weathering events in a karst environment. The age of most deposits appears to be generally confined to the Tertiary, with a distinct period of descloizite formation dated at 24 to 33 Ma. The V ores are genetically related to post-Gondwanan erosional episodes, controlled by tectonomorphological evolution following rifting phases in the Atlantic realm and spanning the period from the end of the Cretaceous to Pleistocene.


ISSN: 0361-0128
EISSN: 1554-0774
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 102
Serial Issue: 3
Title: Genesis of vanadium ores in the Otavi mountainland, Namibia
Affiliation: Universita di Napoli, Dipartimento di Scienze della Terra, Naples, Italy
Pages: 441-469
Published: 200705
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 105
Accession Number: 2007-117277
Categories: Economic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. charts, sects., 8 tables, sketch maps
S20°00'00" - S19°00'00", E17°15'00" - E18°15'00"
Secondary Affiliation: CSIRO, Exploration and Mining, AUS, AustraliaUniversitaet Heidelberg, DEU, Federal Republic of GermanyUniversity of Geneva, CHE, Switzerland
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Society of Economic Geologists. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200748
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