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REE and Sr isotope characteristics of carbonate within the Cu–Co mineralized sedimentary sequence of the Nchanga Mine, Zambian Copperbelt

REE and Sr isotope characteristics of carbonate within the Cu–Co mineralized sedimentary sequence of the Nchanga Mine, Zambian Copperbelt
REE and Sr isotope characteristics of carbonate within the Cu–Co mineralized sedimentary sequence of the Nchanga Mine, Zambian Copperbelt
Carbonate, largely in the form of dolomite, is found throughout the host rocks and ores of the Nchanga mine of the Zambian Copperbelt. Dolomite samples from the hanging wall of the mineralization show low concentrations of rare-earth elements (REE) and roof-shaped, upward convex, shale-normalized REE patterns, with positive Eu*SN anomalies (1.54 and 1.39) and marginally negative Ce anomalies (Ce*SN 0.98,0.93). In contrast, dolomite samples associated with copper and cobalt mineralization show a significant rotation of the REE profile, with HREE enrichment, and La/LuSN ratios <1 (0.06–0.42). These samples also tend to show variable but predominantly negative Eu*SN and positive cerium anomalies and an upwardly concave MREE distribution (Gd-Er). Malachite samples from the Lower Orebody show roof-tile-normalized REE patterns with negative europium anomalies (Eu*SN 0.65–0.80) and negative cerium anomalies (Ce*SN 0.86–0.9). The carbonate 87Sr/86Sr signature correlates with the associated REE values. The uppermost dolomite samples show Neoproterozoic seawater-like 87Sr/86Sr ratios ranging from 0.7111 to 0.7116, whereas carbonate from Cu–Co mineralized samples show relatively low concentrations of strontium and more radiogenic 87Sr/86Sr, ranging between 0.7136–0.7469. The malachite samples show low concentrations of strontium, but give a highly radiogenic 87Sr/86Sr of 0.7735, the most radiogenic 87Sr/86Sr ratio. These new data suggest that the origin and timing of carbonate precipitation at Nchanga is reflected in the REE and Sr isotope chemistry. The upper dolomite samples show a modified, but essentially seawater-like signature, whereas the rotation of the REE profile, the MREE enrichment, the development of a negative Eu*SN anomaly and more radiogenic 87Sr/86Sr suggests the dolomite in the Cu–Co mineralized samples precipitated from basinal brines which had undergone significant fluid–rock interaction. Petrographic, REE, and 87Sr/86Sr data for malachite are consistent with the original sulfide Lower Orebody being subject to a later oxidizing event.
0026-4598
881-891
Roberts, Stephen
f095c7ab-a37b-4064-8a41-ae4820832856
Palmer, Martin R.
d2e60e81-5d6e-4ddb-a243-602537286080
Cooper, Matthew J.
54f7bff0-1f8c-4835-8358-71eef8529e7a
Buchaus, Peter
f45fc31f-901b-42d3-9c3d-73fc0d25088d
Sargent, Drew
ecf2d7da-9861-4926-ac6b-04761323e3c1
Roberts, Stephen
f095c7ab-a37b-4064-8a41-ae4820832856
Palmer, Martin R.
d2e60e81-5d6e-4ddb-a243-602537286080
Cooper, Matthew J.
54f7bff0-1f8c-4835-8358-71eef8529e7a
Buchaus, Peter
f45fc31f-901b-42d3-9c3d-73fc0d25088d
Sargent, Drew
ecf2d7da-9861-4926-ac6b-04761323e3c1

Roberts, Stephen, Palmer, Martin R., Cooper, Matthew J., Buchaus, Peter and Sargent, Drew (2009) REE and Sr isotope characteristics of carbonate within the Cu–Co mineralized sedimentary sequence of the Nchanga Mine, Zambian Copperbelt. Mineralium Deposita, 44 (8), 881-891. (doi:10.1007/s00126-009-0254-2).

Record type: Article

Abstract

Carbonate, largely in the form of dolomite, is found throughout the host rocks and ores of the Nchanga mine of the Zambian Copperbelt. Dolomite samples from the hanging wall of the mineralization show low concentrations of rare-earth elements (REE) and roof-shaped, upward convex, shale-normalized REE patterns, with positive Eu*SN anomalies (1.54 and 1.39) and marginally negative Ce anomalies (Ce*SN 0.98,0.93). In contrast, dolomite samples associated with copper and cobalt mineralization show a significant rotation of the REE profile, with HREE enrichment, and La/LuSN ratios <1 (0.06–0.42). These samples also tend to show variable but predominantly negative Eu*SN and positive cerium anomalies and an upwardly concave MREE distribution (Gd-Er). Malachite samples from the Lower Orebody show roof-tile-normalized REE patterns with negative europium anomalies (Eu*SN 0.65–0.80) and negative cerium anomalies (Ce*SN 0.86–0.9). The carbonate 87Sr/86Sr signature correlates with the associated REE values. The uppermost dolomite samples show Neoproterozoic seawater-like 87Sr/86Sr ratios ranging from 0.7111 to 0.7116, whereas carbonate from Cu–Co mineralized samples show relatively low concentrations of strontium and more radiogenic 87Sr/86Sr, ranging between 0.7136–0.7469. The malachite samples show low concentrations of strontium, but give a highly radiogenic 87Sr/86Sr of 0.7735, the most radiogenic 87Sr/86Sr ratio. These new data suggest that the origin and timing of carbonate precipitation at Nchanga is reflected in the REE and Sr isotope chemistry. The upper dolomite samples show a modified, but essentially seawater-like signature, whereas the rotation of the REE profile, the MREE enrichment, the development of a negative Eu*SN anomaly and more radiogenic 87Sr/86Sr suggests the dolomite in the Cu–Co mineralized samples precipitated from basinal brines which had undergone significant fluid–rock interaction. Petrographic, REE, and 87Sr/86Sr data for malachite are consistent with the original sulfide Lower Orebody being subject to a later oxidizing event.

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Published date: November 2009

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Local EPrints ID: 69684
URI: http://eprints.soton.ac.uk/id/eprint/69684
ISSN: 0026-4598
PURE UUID: 701b1dde-f51a-4050-a542-b708469950e2
ORCID for Stephen Roberts: ORCID iD orcid.org/0000-0003-4755-6703
ORCID for Matthew J. Cooper: ORCID iD orcid.org/0000-0002-2130-2759

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Date deposited: 25 Nov 2009
Last modified: 14 Mar 2024 02:45

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Author: Stephen Roberts ORCID iD
Author: Peter Buchaus
Author: Drew Sargent

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