Moxico Resources owns 100% of Excelsior, a zinc occurrence discovered in the early 1920s
Excelsior is a high grade zinc silicate occurrence with grades up to 40% zinc outcropping at surface. The prospect has been explored intermittently in the past but has yet to undergo systematic exploration in more recent times. Moxico plans to carry out closely spaced soil sampling and geological mapping, followed by trenching and drilling of the mineralization with the aim of defining an economic zinc resource after which a mining license can be granted with 25 year validity.
During the mid 2000s, TEAL Zambia Limited held the prospecting rights the Excelsior prospect, one of the most important zinc occurrences in the Lusaka area. Mineralogical, petrographic and geochemical analyses were carried out by by Terracciano in 2008 and by Boni et al in 2010 to characterize this unusual ore type. The results indicate that the high-grade Zn-silicate concentrations of the Zambezi Belt have many similarities with those hosted by the Franklin Marbles of the Greenville Province in New Jersey (USA) as exemplified by the Franklin and Sterling Hill deposits
LOCAL GEOLOGY AND MINERALISATION
The Excelsior prospect (Matthews 2003 cited in Boni et al 2010) consists of a number of mineralized localities dispersed over an area of 5×5 km, comprising zinc silicate (willemite) pods. The willemite pods are located in a complexly altered and brecciated carbonate sequence surrounded by unaltered banded limestone and dolostone. Eight different mineralized pods over an area of approximately 25 km2 have been found (Matthews, 2003). The individual pods are small - less than 10 m in diameter, though extremely high grade, with boulder-sized samples composed entirely of willemite with grades of up to 53% Zn.
Specular hematite is commonly intergrown with the willemite ore, and significant amounts of native silver have been found as well (Spencer 1927; Sweeney et al. 1991 both cited in Boni et al 2010). High-grade zinc zones may be enriched in silver in the form of fine-grained disseminations intergrown with the willemite crystals. Spectacular native silver dendrites, wires and blebs are also found within calcite and/or quartz veins. Traces of germanium and cadmium were reported by Sweeney et al. (1991) cited in Boni et al 2010 within the ore. It was reported that the mineralisation averages 40% Zn and 78 g/t Ag (Freeman, 1989 cited in Boni et al 2010).
Excelsior contains the zincian spinels gahnite and franklinite (i.e. Zn-aluminate and Zn-ferrite, respectively; Lucchesi et al. 1998, 1999 cited in Boni et al 2010), and willemite, paragenetically associated with specular hematite. Willemite occurs as a low-tonnage, high-grade carbonate-hosted concentration.
According to Sweeney et al. (1991) cited in Boni et al 2010 the willemite concentrations at Excelsior frequently extend beyond the bedded horizons along joints and fissures. The deposit displays locally zebra-like and colloform textures. The joints are filled with willemite (plus carbonates, clinochlore— and barite), thus giving the impression that the small orebodies are vein-hosted (Sweeney et al. 1991). Open-space filling textures at the contact with the host rock were regarded by Sweeney et al. (1991) cited in Boni et al 2010 as infill of old karstic solution features. Karst fill deposits (Tertiary to Recent?) and red soils (terra rossa) are locally heavily mineralised with detrital willemite (Matthews, 2005 cited in Boni et al 2010) and supergene zinc minerals.
ACQUISITION AND PLANS
The Excelsior licence is 100% owned by Moxico Resouces plc through its subsidiary Moxico Resources Zambia Ltd under Large Scale Exploration License number 21257-HQ-LEL valid until 2021. Moxico plans to carry out closely spaced soil sampling and geological mapping, followed by trenching and drilling of the mineralization with the aim of defining an economic zinc resource after which a mining license can be granted with 25 year validity.