Geochemistry and secondary alterations of microlite from aluvial deposits in the Numbi area, S. Kivu, Democratic Republic of the Congo

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00216224%3A14310%2F18%3A00102881" target="_blank" >RIV/00216224:14310/18:00102881 - isvavai.cz</a>

Result on the web

<a href="https://pubs.geoscienceworld.org/canmin/article-abstract/56/2/203/529950/geochemistry-and-secondary-alterations-of?redirectedFrom=fulltext" target="_blank" >https://pubs.geoscienceworld.org/canmin/article-abstract/56/2/203/529950/geochemistry-and-secondary-alterations-of?redirectedFrom=fulltext</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.3749/canmin.1700091" target="_blank" >10.3749/canmin.1700091</a>

Result language

angličtina

Original language name

Geochemistry and secondary alterations of microlite from aluvial deposits in the Numbi area, S. Kivu, Democratic Republic of the Congo

Original language description

Microlite and U-enriched microlite were found in eluvium close to highly weathered granitic pegmatites actively mined as a source of tantalum ore and situated within the ~1000–900 Ma old Kibara belt unit, Numbi mining area, South Kivu province of the Democratic Republic of the Congo. Two examined pegmatites differ in their mineral assemblages and in the degree of fractionation: in the Mungwe pegmatite (lepidolite subtype) cassiterite, microlite-group minerals (microlite, U-enriched microlite), columbite-group minerals (columbite–tantalite), wodginite, ferrotapiolite; at the Misumari II pegmatite (beryl-columbite subtype) microlite, cassiterite, columbite–tantalite, wodginite–ferrowodginite. Both pegmatites underwent deep tropical weathering; however, the degree of hydrothermal alteration of the (Nb,Ta)-oxide minerals is rather low. Fragments of primary microlite and U-enriched microlite (the latter present only at the Mungwe pegmatite) are mostly homogeneous and compositionally uniform; locally U-enriched microlite forms outer zones of the grains. Primary microlite from the lessfractionated Misumari II pegmatite is rather homogeneous and has Ta/(Ta+Nb)=0.74–0.94 and higher Ti=0.07–0.23 apfu at the B-site compared to the Mungwe pegmatite with similar Ta/(Ta+Nb)=0.82–0.88 and low Ti. Microlite from Misumari II has higher contents of almost all trace elements (including REE) except for Li, Sb, and Pb. Primary microlite from both sites has Ca/Na close to 1, low A-site vacancy, and high F. Uranium-enriched microlite shows 0.29 apfu U, moderate A-site vacancy, and lower concentrations of F. Alteration of the U-poor microlite is very limited compared to the U-enriched microlite where radiation damage disrupted the mineral structure prior to the alteration. The altered microlite is depleted in Na and F and has high vacancy at the A-site, but the B-site population is almost identical to that of the primary microlite, as are the U concentrations. Such a composition is typical for secondary low-T alterations related to weathering. We demonstrate that the combined results from Automated Mineralogy, Electron Microprobe Analysis, and LA-ICP-MS techniques (along with the specific alteration features) can be successfully used to prove the provenance of tantalum ore by comparison with other localities where microlite is a major Ta-bearing mineral.

Czech name

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Czech description

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Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

—

OECD FORD branch

10504 - Mineralogy

Project

—

Continuities

S - Specificky vyzkum na vysokych skolach

Publication year

2018

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Name of the periodical

Canadian Mineralogist

ISSN

0008-4476

e-ISSN

—

Volume of the periodical

56

Issue of the periodical within the volume

2

Country of publishing house

CA - CANADA

Number of pages

18

Pages from-to

203-220

UT code for WoS article

000451742400008

EID of the result in the Scopus database

2-s2.0-85054182943