Re-Os age report of pyrrhotite in the Dhi Samir amprophyre-type copper-nickel sulfide deposit in Yemen

1.   Objectives

The Dhi Samir copper-nickel sulfide deposit is located in the Taiz Province, South Yemen. The ore-bearing rock bodies occurred in the Neoproterozoic magmatic veins (Fig. 1). Different from most magmatic copper-nickel sulfide deposits, the Dhi Samir copper-nickel deposit is produced in the lamprophyre rather than in the mafic-ultramafic rocks such as peridotite, norite and gabbro. The main rock type is calcium-alkaline lamprophyre. In 2011, the authors reported that the zircon LA-ICPMS U-Pb isotopic age of ore-bearing lamprophyre is 602 Ma (Zuo LY et al., 2011), representing the diagenesis age of the lamprophyre. Now, this paper use the Re-Os isotope method to determine the metallogenic age of the copper-nickel deposit.

Figure  1.  Geological map of the Dhi Samir Cu-Ni deposit in Yemen.

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2.   Research methods

Fresh samples of massive ore was taken from the tunnel and core. Unpolluted pyrrhotite powders were selected to meet the test standards. The experiment was completed by the Re-Os isotope Laboratory of the National Reserach Center for Geoanalysis. Measurements were carried out using a high resolution inductively coupled plasma mass spectrometer ELEMENT2 HR-ICP-MS. The Os was calculated from the atomic scale and the isotope abundance table (Wieser, 2006) by a measurement ratio of ¹⁹²Os/¹⁹⁰Os. The experimental measurement error confidence level was 95%, the uncertainty of the model age also included the uncertainty of the decay constant (1.02%), and the confidence level was 95% (Qu WJ et al., 2003).

3.   Results

The results of Re-Os isotope measurement of 8 massive and densely disseminated ore samples from the Dhi Samir deposit are listed in Table 1. The Re-Os isotope age of pyrrhotite is obtained 578 ± 12 Ma (Fig. 2), indicating that the Dhi Samir copper-nickel ore was formed in the early Neoproterozoic, nearly 20 Ma away from the lamprophyre diagenetic age of 602 Ma.

Table  1.  Re-Os isotope data of the pyrrhotite in the Dhi Samir copper-nickel sulfide deposit.

Sample No.	Sample description	Sample weight /g	$w_{{\rm{Re}}}$/10−9	2σ	$w_{{\rm{Os}}}$/10−9	2σ	$w_{{187}_{{\rm{Re}}}}$/10−9	2σ	187Re/188Os	2σ	187Os/188Os	2σ
Zk002-8	Dense disseminated ore	0.301	29.73	0.24	0.3964	0.0036	0.1985	0.0019	362.3	4.4	3.849	0.033
Y2-9	Massive ore	0.397	18.15	0.24	0.039	0.0017	0.1169	0.0013	2250	102	23.06	1.01
Y2-3	Massive ore	0.410	4.50	0.07	0.0918	0.0018	0.032	0.0005	237	5.9	2.679	0.06
Zk401-5	Massive ore	0.399	12.32	0.13	0.035	0.0012	0.0774	0.0009	1701	60	17	0.59
Y1-2	Massive ore	0.400	11.63	0.15	0.215	0.003	0.082	0.0009	261.3	4.9	2.931	0.042
Zk002-9	Massive ore	0.394	50.70	0.54	0.2431	0.0032	0.3181	0.0034	1007	17	10.06	0.14
Zk1201-14	Massive ore	0.398	17.90	0.19	0.0776	0.0017	0.1119	0.0013	1114	27	11.08	0.25
Zk1201-16	Dense disseminated ore	0.406	11.98	0.13	0.0296	0.0007	0.0345	0.0004	1953	49	8.957	0.209
Note: Analysed by National Research Center for Geoanalysis, China Geological Survey.

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Figure  2.  Re-Os isotope isochronism of pyrrhotite in Dhi Samir copper-nickel sulfide deposit.

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4.   Conclusion

In the previous study, the lamprophyre diagenetic age of the Dhi Samir was 602 Ma. In the present study, the Re-Os isotopic age of the pyrrhotite in the Dhi Samir copper-nickel deposit was 578 Ma, and the diagenetic and ore-forming ages are nearly 20 Ma. It indicates that the magma and the ore pulp are from the same source area and are the products of Pan-African orogenic tectonic magma event.

5.   Acknowledgement

This paper is the result of the funded project of the Yemen Resources Group's Yemen Project Team and China Geological Survey's National Geological Survey Results Integration and Planning Project (DD20190464).