4.   MINERAL RESOURCE AND RESERVES

4.5.1  

Rosh Pinah

Drilling at Rosh Pinah is divided into primary, secondary and tertiary phases. The primary and secondary drilling are exploration drilling used to find and broadly delineate the orebodies. The tertiary drilling is used to more accurately define the limits of the orebody for production planning and to obtain closely spaced grade information for estimation purposes.

The exploration drilling at Rosh Pinah is predominantly conducted from underground exploration drives developed alongside the orebody, or the expected position of the orebody. The primary drilling is conducted on a 60m grid and the secondary drilling on a 30m infill grid. The tertiary drilling is drilled from production drives within the orebody and from access tunnels near the orebody and attempts to obtain a 10m grid of pierce points through the margins of the orebody limits, as well as creating a grid of grade values within the orebody. Since the geometry, width and shape of the orebodies are highly irregular, it is not always possible to conform to a precise grid and thus the drilling can better be described as 60m-, 30m- and 10m-spaced pierce points drilled perpendicular to orebody attitude. Surface drilling is also conducted at Rosh Pinah. Over the history of the mine, there has been a total of over 400,000m drilled. Of that, approximately 100,000m was drilled from surface, 184,000m from underground as primary and secondary exploration and 120,000m as tertiary production drilling.

All underground drilling is currently with BQ sized diamond drill core (42.1mm). However in the past some NQ (54.8mm) sized core was drilled, predominantly from surface to gain the maximum benefit from oriented core and structural information. Core recoveries are recorded on the log sheets and are generally reported to be in excess of 95%. Some reverse air blast drilling has also been conducted in the past on soil covered plains to determine bedrock lithology and obtain a rock chip sample. Secondary underground boreholes that are less than 100m in length have co-ordinate positions calculated according to surveyed collar dips and azimuths; all boreholes over 100m in length are surveyed using down-hole survey equipment. All the holes are electronically logged and photographed for lithological and structural information before being sampled. Samples are taken across any mineralised area. The maximum length of a sample is 1.5m with a minimum length of 40cm. Samples are not taken across lithological boundaries and a 1.5m waste envelope is sampled beyond the interpreted extent of the mineralised zone. The exploration drill core is halved with a diamond saw for sampling while the entire core is sampled for the tertiary drilling. The drilling and assay results are stored in a database, using acQuire software as a front end. The software has a number of validation procedures that insure integrity of the input information in terms of duplicate entries, overlaps and gaps in the drillhole information. Historical drillhole information that has been added to the acQuire database is also in the process of being checked and verified.

Samples are bagged and sent to the on-mine assay laboratory for analysis. Since Rosh Pinah is a Nambian mine, its laboratory does not fall under the ambit of SANAS. The laboratory also does not comply with an ISO accreditation. However, the mine has been operational since 1970 and the on-mine assay laboratory has provided a reliable service in this time.

At the laboratory, the core is crushed with a jaw crusher and then split with a Jones riffle. SRK did not observe the sample preparation in progress, but did however see the discards from the riffle splitter. Some of the material was, in certain dimensions, wider than the ‘slots’ in the riffle splitter. The distribution of metal within the ore at Rosh Pinah is quite heterogeneous and coarse material such as this can lead to significant bias. The ‘slots’ in the riffle were also unevenly sized, and had a different number of slots for the two sides, which can lead to a bias in the splitting. There is a secondary crusher available at the sample preparation site which is apparently currently not in use. Comminution to a smaller size would significantly reduce the potential for the process to introduce bias to the preparation procedure. The selection from the riffle splitter is then milled in a rotary puck mill to <45µm, and laid out on a sheet, where several random scoops are taken to be composited for analysis.

A 0.1g aliquot of the pulp is dissolved in Aqua Regia (a mixture of Nitric Acid (HNO₃) and Hydrochloric Acid (“HCl”), filtered and then analysed by Atomic Absorption Spectrometry (“AAS”). Total zinc, lead, copper, Fe and Mg concentration are determined and sulphide zinc and lead are derived from the difference of oxide from the total. Recently the Mine Laboratory has acquired an Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) which is currently being used in conjunction with the AAS for the zinc and lead assays. The reject pulps are returned to the geology department for reference.

The geology department does not submit any independent control samples, however the laboratory analyses a standard sample and a blank sample at the start of every batch. After every 10 samples, the blank and the standard sample as well as the first sample in the batch are repeated. On a monthly basis metallurgical samples are exchanged with two other laboratories (SGS and Industrial Analytical) to verify the accuracy of the results; 132 sample assays have been repeated at Anglo American Research Laboratories (“AARL”) in South Africa. The Rosh Pinah results tended to be lower than the AARL analyses. Individual orebodies are defined to constrain grade estimation to the defined mineralised horizons by developing outlines of the orebodies on sections based on the drillhole intersections. The primary data used from the drill holes to derive these outlines are the metal grades. A cut-off of 4% combined zinc and lead is used for the ore outline definition. In addition, outlines of several lithologies within the mineralised envelope are defined. In most areas vertical sections are used primarily to define the outlines, with plan sections used as controls between the vertical sections, with the exception of the A Mine and Eastern Ore Field (“EOF”) where plan views are the primary definition, and the vertical sections are used as controls because the orebodies plunge very steeply. Wireframe models are created for each of the lithologies within the mineralised envelope by joining each of the outlines on each section together. The wireframes are used to create block models for each orebody, with cell dimensions of 5m x 5m x 5m, and to assign each block with a ‘percent in ore’ value. An average Relative Density (“RD”) of 3.0 t/m³ is assigned to all the orebodies with the exception of the EOF, which is allocated a RD of 3.46 t/m³. The higher average RD used for the EOF is based on the higher average metal grades found in the EOF, and a set of approximately 3,000 relative density measurements which averaged at 3.46 t/m³ for the EOF, and 3.0 t/m³ for the remaining orebodies. The drillholes are composited over 1.5m lengths from the collar. Unsampled intervals that occur within the orebody are assigned a zero value. Anisotropic semi-variograms are calculated for each orebody and where applicable to sub-divided domains within the individual orebodies. The directions of the longest ranges are determined from contour plots of the variograms.

The Rosh Pinah Resource and Reserve Statement is SAMREC compliant.

Table 4.24