2010-12-17_REVISION - C1981019 (130)

Home Browse Search

shell, derived by strip ratio analysis, has been developed to include 17 coal seams with total in situ coal of 176M tons. Seams have been included in the planning reserve on the basis of criteria for Minimum Mining Thickness (2 feet) and coal quality (9,500 BTU, 10% ash and 1.2 Ibs/ mmBTU sulphur). An initial Collom boxcut is proposed at the northern end of the resource area with mining proceeding up dip towards the south, similar to the approach successfully employed in the current CCC mining area. This generally involves mining higher strip ratio areas first, but offers the advantage of shorter haulage to the proposed out of pit waste stockpile location. Although the 2003 CRS Collom mine plan involved a combination of dragline and truck/shovel mining methods, the most recent mine plan has adopted a truck/shovel only method due to increased flexibility and reduced requirement for out of pit dumping. Whilst the rationale for mine planning decisions to date has been described in project documentation, it is not evident that the Collom mine plan options have been rigorously evaluated to identify and demonstrate the optimal economic choices. One of the expectations of the Pre - Feasibility stage of project development is that the range of feasible options and alternatives are evaluated to "...resolve questions over project scale and scope, so the design concepts can be frozen. A Pre - feasibility Study therefore generally describes the project that will be built, rather than one which is conceptual only or still contains major options. " Further mine planning work is required to resolve key questions on project scale, economic pit limits, mining direction and sequence and mining methods. This work should be based on the latest geological, geotechnical and hydrology data after completion of the current exploration program. Such work is considered a prerequisite to complete the Collom Pre - Feasibility Study. As outlined in the Rio Tinto Energy Mine Planning Guidelines (Open Cut Coal) the preferred approach for definition of pit limits (including basal seams) and guidance of the optimal mining sequence is economic margin ranking, not strip ratio analysis. A margin ranking study should also assist in evaluation of project scale, boxcut location, mining direction and mining methods. TS recommend CCC undertake a margin ranking study on the Collom resource after completion of the current exploration program. Mining recovery for Collom has been assumed to average 90.1%, but the basis for this assumption is not evident. No explicit allowance for dilution is evident. TS recommends CCC develop and document the basis for mining recovery assumptions and include a specific allowance for dilution. It would be expected that these assumptions would vary on a seam by seam basis. Again reference should be made to the Mine Planning Guidelines for the preferred approach. The Colowyo topography features a series of parallel ridges and deeply incised drainage channels running on a south west to north east orientation. The proposed Collom pit spans two such ridges and includes the ephemeral Little Collom Gulch drainage, which is 200 to 300 feet deep over most of the mining area. Mining is planned to generally progress to the . south west up towards the head of the drainage. The most recent mine design incorporates RIO TINTO TS Ref: DRAFT Version: 1 12 Technical5crvices