Characterizing the fungurume 88 deposit in the tenke fungurume mining district: an unusual, high-grade, primary cobalt sulphide deposit

Date
2021-12
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: The Tenke Fungurume Mining (TFM) district, situated in the northern parts of the Central African Copperbelt (CACB), exhibits one of the most renowned clusters of sedimentary stratiform copper deposits across the globe. The Fungurume 88 deposit comprises one of these clusters and is also described as a Roan-cored escallies (or tectonic window) and is situated in the south-east of the TFM district. It does not outcrop anywhere but is juxtaposed against the overlying Fungurume 8 deposit. Drill core logging and assaying of holes that intersected both the Fungurume 8 and 88 deposits have indicated that the two deposits exhibit uniquely different Cu-Co grades. Furthermore, they show variation in host lithologies although exhibiting the same sequence stratigraphy. A particular difference and one which forms the major underpinning of this study is the presence of extremely high-grade cobalt mineralization in the form of carrollite (CuCo2S4) hosted within a dolomitic shale/mudstone of the SD- 1b subunit within the Fungurume 88 deposit. This subunit is typically barren in the Fungurume 8 deposit which in turn is composed of a dolomitic sandstone/siltstone. Moreover, the Fungurume 8 deposit along with the majority of deposits in the TFM district have been identified to exhibit sediments belonging to the Long Facies. Petrographic studies on the SD-1b subunit in the Fungurume 88 deposit revealed numerous sulphide textures including the stratiform, disseminated, jack vein and cross-cutting vein mineralization. The morphological traits observed have allowed these mineralization styles to be distinguished in a temporal context whilst LA-ICPMS trace element assessment has also allowed the geochemical grouping of these episodes of mineralization. These groupings of mineralization include an early (probably diagenetic) episode as well as a later (probably syn-tectonic) episode. Petrographic studies of the host rock not only confirm that the Fungurume 8 deposit exhibits sediments of the Long facies but reveal that the sediments of the Fungurume 88 deposit belong to a deeper water sedimentary facies – likely the Kalumbwe or Menda facies. These insights corroborate with thermodynamic modelling of Cu and particularly Co phases, have also proposed reasons for the metal segregation and zonation we see within the Fungurume 88 deposit. From the entire hypogene mineral suit of the CACB, carrollite is the dominant host for cobalt metal. Interestingly, however, there is little known about its geochemistry, crystallography and surface properties. Another avenue of this study addresses these aspects revealing the trace element contents of carrollite along with their effects on the structural configuration and surface chemistry. Overall, the carrollite samples studied here are Cu-rich and exhibit a unit cell parameter of 9.4845 Å. From the data presented in this study, the thermodynamic analysis, crystallographic data and Raman spectroscopy (surface chemistry) represent the first of their kind for naturally occurring carrollite samples. This data in conjunction with major and trace element geochemistry as well as petrography provides a description of as well as genetic model for, the Fungurume 88 deposit.
AFRIKAANSE OPSOMMING: Die Tenke Fungurume Mynbou (TFM) distrik is geleë in die noordelike dele van die Sentraal - Afrikaanse Koperbelt (SAKB) en vertoon een van die bekendste groep sedimentêre laagvormige koperafsettings regoor die wêreld. Die Fungurume 88 afsetting bestaan uit een van hierdie groepe, wat ook beskryf word as 'n tektoniese venster en wat in die suidooste van die TFM-distrik geleë is. Dit dagsoom nêrens nie, maar is in kontak met die boonste Fungurume 8 afsetting. Boorkern beskrywing en essai van boorgate wat beide die Fungurume 8 en 88 afsettings deurgedring het, het aangedui dat dié twee afsettings verskillende Cu-Co-grade vertoon. Verder, toon hulle variasie in herberggesteentes, alhoewel hulle dieselfde volgorde van die stratigrafie vertoon. 'n Opmerklike verskil en een wat die fondasie van hierdie ondrsoek vorm, is die teenwoordigheid van 'n uiterse hoëgraadse kobaltmineralisering in die vorm van (CuCo2S4) wat in 'n dolomitiese skalie/moddersteen van die SD- 1b subeenheid in die Fungurume 88 afsetting gehuisves word. Hierdie subeenheid is gewoonlik die bar gesteentes van die Fungurume 8 afsetting wat uit 'n dolomitiese sandsteen/sliksteen bestaan. Die Fungurume 8 afsetting, saam met die meerderheid ander afsettings in die TFM-distrik is geïdentifiseer om uit sedimente wat deel vorm van die Long fasies te bestaan. Petrografiese ondersoek oor die SD1b- subeenheid in die Fungurume 88 afsetting het talle sulfiedteksture geopenbaar, insluitend die stratiforme, gedissemineerde, ‘jack’ aar en dwarsgangende aar mineralisering. Die morfologiese eienskappe van hierdie verskillende teksture het hierdie mineraliseringsstyle in 'n tydelike konteks laat onderskei, terwyl LAICPMS spoorelementassessering ook die groepering van hierdie mineralisering episodes vanuit 'n geochemiese oogpunt moontlik gemaak het. Hierdie groeperings in ‘n mineralisering oogpunt, sluit 'n vroeë (waarskynlik ‘n diagenetiese) episode sowel as 'n latere (waarskynlik ‘n sintektoniese) episode in. Petrografiese ondersoek van die herberggesteentes het nie net bevestig dat die Fungurume 8 afsettings sedimente van die Long fasies vertoon nie, maar het aan die lig gebring dat die sedimente van die Fungurume 88 afsetting deel vorm van die dieper watersedimente fasies behoort - waarskynlik die Kalumbwe of Menda fasies. Hierdie bevindings bevestig, sowel as termodinamiese modellering van Cu en veral Co fases, die metaalsegregering en sonering wat in die Fungurume 88 afsetting voorkom. Uit die hele verskydenheid hipogeen mierale van die SAKB, is “carrollite” die dominante herberg vir kobalt. Interessant genoeg is daar min kennis oor die geochemie, kristallografie en oppervlakteienskappe daarvan. Hierdie ondersoek spreek hierdie onbekende aspekte van “carrollite” aan, wat die spoorelementinhoud van “carrollite” openbaar, asook die effek daarvan op die strukturele opset en oppervlakchemie van “carrollite. In die algemeen is die “carrollite” monsters wat hier bestudeer word, Cu-ryk en vertoon 'n eenheid selparameter van 9.4845 Å. Vanuit die bevindings wat in hierdie ondersoek voorgestel word, verteenwoordig die termodinamiese analise, kristallografiese data en Raman-spektroskopie (oppervlakchemie) vir natuurlik voorkomende “carrollite” monsters en in samewerking met hoof- en spoorelementgeochemie sowel as petrografie, die ontstaan van die Fungurume 88 afsetting word goed beskryf.
Description
Thesis (MSc)--Stellenbosch University, 2021.
Keywords
Tenke Fungurume mining -- Central Africa -- Copperbelt, Cobalt mines and mining, Sedimentary stratiform copper deposits, Cobalt ores, UCTD
Citation