Higher_Education_Should_Be_Funded_by_the_State

Assignment no. 2 eEveline KEKANA Mining and exploration Geology IV Student no. 209027135 19 August 2013 Goldfields South Deep Mine Sampling procedures for grade control and ore reserve estimation. The South Deep underground gold mine is situated approximately 45km southwest of Johannesburg and is established in the Witwatersrand Basin to exploit the Venterdorp Contact Reef, the upper and lower Elsburg reefs. The Central Rand Group hosts most of the gold bearing conglomerates and is thought to have deposited in a more restricted basin, specifically in a foreland tectonic setting and is dominated by fluvial braid plain deposits, however trangressive shallow marine sandstones are commonly noted in close association. The Elsburg reef at South Deep comprise of the following reefs at South Shaft: EB, ECBA, ECBAQ, ECB, ECBQ, ECMC, ECMQ, ECT, ED, MAC, MAS, MAD, MIT, MIC, MBB, MBT, VCR and LAVA. The UE’s are also found at the Twin Shaft at South Deep. A coarse conglomerate facies comprises a high proportion (>70%) with large to cobble sized clasts and host economic gold mineralisation within all reefs while a sandy conglomerate facies comprises a low proportion (<30%) with small to medium clasts and host uneconomic gold concentrations. The high potential geological domains closely follow the lobes of coarse conglomerates while low potential geological domains follow the lobes of poor and sandy conglomerates. High gold grade can be associated with poor sedimentary concentrating processes such as debris flow deposits. The behaviour of gold grades in different areas relates to the broadly homogeneous areas as recognized through the changes in the regression factors. Parameters indicating gold concentration are lithofacies, packing, pebble size, pebble assemblage, type of pyrite, amount of pyrite and pyrite grain size. Better concentrations of gold are usually found in well packed, pebble supported conglomerate, oligomictic, massive conglomerates with a high amount of pyrite. Sampling procedure of the mine occurs in five steps: 1. Breaking the core and marking off the sample intervals; 2. Placing the sample tickets; 3. Preparing of the QA/QC samples 4. Bagging the core samples ; 5. Creating a manifest of the samples in DH logger. 1. Breaking the core and marking off the sample intervals. * Clean and align the core. * Select mineralized sections to be sampled. These to include complete sections through known economic horizons (VCR, MBT, MBB, MAC, ECT etc.). Other mineralized sections (e.g., ECB ,ECBA etc.) to be selectively sampled * Core of the Elsburg reefs is sampled continuous from the bottom of the EC to the lava intersection. The ED’s which is known to be barren, may be sampled in larger intervals of up to 1m. * After deciding which part of the core should be sampled, the core may be marked at sample intervals. * The beginning of the core that needs to be sampled must be marked. * Measure of ~20 to 30cm form the start position. * If there is a break in the core close to 30cm from the start, use this break as the end of your first sample interval. * If there is no break in the core where you would like the end of the interval, break the core and then mark of the break position, to ensure that your markings are always exactly on the beginning and end of the intervals you want to sample. * The process is carried until all the core you want to sample is marked off. * A sample interval on the core must not be marked where there is no break in the core and then try to break it in that position afterwards. The core will not necessarily break on the position you marked and this can lead to errors when you log the sample intervals into DH logger. * In holes with only VCR and no Elsburg core, only the VCR core is sampled in intervals of ~30cm. The footwall quartzite is not sampled unless there are zones which are visibly well mineralized (i.e. the UE1, -3 or -4 conglomerates). * Cover holes with reef intersections are sampled similar to the exploration holes, but with larger sample intervals. In cover holes drilled at +/- 5°, sample intervals can be increased to 1.5m. * Cover holes, holes that are drilled specifically to resolve structure or the footwall stratigraphy, or other holes without any reef intersections are not sampled. * In the case of holes with a reef intersection as well as footwall quartzite and/or lava, 2 samples are taken of the footwall directly below the reef and or 2 samples of the lava directly above the reef. This is to ensure that the full mineralized zone is sampled, as the top and bottom contacts of the reef are often well mineralized (See Example 1 & 2). Example 1: A Typical Example of Sample Intervals on the VCR Hole with Footwall Quartzite and Lava | Smp. 1 | Smp. 2 | Smp. 3 | Smp. 4 | Smp. 5 | Smp. 6 | Smp. 7 | Smp. 8 | Smp. 9 | | |   |   |   |   |   |   |   |   |   | | | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | |   |   |   |   |   |   |   |   |   |   |   | UE2 Quartzite | VCR | Lava | Example 2: Sample Intervals on a drill hole through the Elsburg Reefs (with EB quartzites below the EC’s and Lava above the VCR. Please note that the diagram is not to scale and is not representative of the actual reef thicknesses. | Smp. 1 | Smp. 2 | Smp. 3 | Smp. 4 | Smp. 5 | Smp. 6 | Smp. 7 | Smp. 8 | Smp. 9 | Smp. 10 | |   |   |   |   |   |   |   |   |   |   | | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm |   |   |   |   |   |   |   |   |   |   |   | EB | EC | | | | | | | | | | | | Smp. 11 | Smp. 12 | Smp. 13 | Smp. 14 | Smp. 15 | Smp. 16 | Smp. 17 | Smp. 18 | Smp. 19 |   |   |   |   |   |   |   |   |   | ~50cm | ~50cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm |   |   |   |   |   |   |   |   |   |   |   | ED | MA | MI | | | | | | | | | | | | Smp. 20 | Smp. 21 | Smp. 22 | Smp. 23 | Smp. 24 | Smp. 25 | Smp. 26 | Smp. 27 | Smp. 28 | Smp. 29 | |   |   |   |   |   |   |   |   |   |   | | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | ~30cm | |   |   |   |   |   |   |   |   |   |   |   | MB | VCR | | Lava | 2. Placing the sample ticket Each sample is given a number which can be traced to the exact position in the specific borehole from which it was taken. To ensure that there is no duplication of numbers, the sample tickets are used. The tickets are printed with water resistant ink on rolls of perforated, wet strength paper. Each number consists of 2 letters and four digits. The letters is the same for the entire roll of tickets, while the digits gives a unique number i.e. numbered from DJ1500 to DJ2000 on a specific roll (figure 1). * GREEN Bar-coded sample tickets with unique numbering will be utilized at all times for borehole sampling purposes – no Mine Paper printed tickets will be acceptable. FIGURE 1: Example of Sample Tickets for Drill Core Samples * Start at the beginning of the marked off sample intervals and place a sample ticket at the beginning of each sample interval. Always check the number of each ticket as you place it, as there might be errors on the sample tickets (e.g. duplicate numbers). * Some of tickets are kept aside for a QA/QC sample (keep these tickets in numerical order, especially when there are many samples). * The tickets must be taken care of so that they are not mixed or lost in the process, they must be recorded on the DH logger or on paper. 3. Preparing the QA/QC samples The QA/QC samples comprise of blanks and standards which are added to every batch of samples send to the lab. This enables to check if the results received from the lab is accurate. At the lab the samples are analysed in batches of 20 at a time. Our aim is to include one standard and one blank in with every 20 samples dispatched to the lab. * Take the first number that was set aside and add it to a sample bag with blank material. A very siliceous quartzite that was analysed and proofed to have a very low gold content is used as a blank. This quartzite is available in the big square bags in the core yard (Figure 2) Record the blank with the ticket number immediately in DH logger. If the blank cannot be recorded directly into digs, write the ticket number down and enter it into DH logger as soon as possible. FIGURE 2: Coarse Quartzite Samples Used as Blanks for the Drill Hole QA/QC Program * The second number that was set aside should be allocated to a standard. The standards used are internationally approved standard powders with known gold contents. The standards used at any time are always kept on the shelves on the left hand side of the pulp storage room as you enter it (Figure 3). There are signs with the standard numbers on the shelves. Select a standard from the shelves and place it in a sample bag with the ticket that was set aside for the standard. NB: Record the standard number with the ticket number immediately DH logger immediately. * Continue taking alternating blank and standard samples until you have used all the sample tickets set aside for QA/QC samples. If you use more than one standard, alternate the standards you select so that you use all the standards and not the same one over and over. Take care to record the numbers of the standards used accurately. Avoid having a blank or a standard as the first or last sample from a borehole. * If there are less than 20 samples from one borehole, there should still be a blank and a standard included with the samples form that borehole. Randomly select 2 tickets and use one for a blank and one for a standard. Avoid having a blank or a standard as the first or last sample from the borehole. FIGURE 3: Standards Used for the Drill Hole QA/QC Program 4. Bagging the core samples Once all the core samples are logged into DH logger they can be bagged. It is important to remember that our Geological Process requires that samples should be bagged by the geologist and not by an assistant. If an assistant helps with the bagging of the core it should be under direct supervision of the responsible geologist. * Start at the beginning the borehole and place each marked off sample with its sample ticket in a sample bag. Take care to stick to the recorded sample intervals, especially when a sample continues from one row of core to the next of from one tray to the next. * Each sample bag is sealed with the sealer (Figure 4) in the pulp storage room to ensure that samples cannot fall out of the bags and get lost or mixed up when transported to the lab. * The sealed samples are packed together in the pulp storage room. Once a sample manifest is added to the samples, it will be dispatched to the lab by the core yard assistants. FIGURE 4: Bag-sealer Used to Seal the Sample Bags 5. Creating a Sample Manifest in DH logger. The sample manifest is in essence a sample list that is send to the lab with the samples. A copy of the sample manifest of each borehole is filed with the layout, assay results and survey results. The purpose of the manifest is to keep record of the samples send to the lab in case there are any queries. It also allows the lab to check and confirm that they did receive all the samples that was send. The sample manifest is created from the sample browser. A copy of manifest is filed with other boreholes in the “Current Boreholes” file. The manifest is taken to the core yard and leaved with bagged and sealed samples in the pulp storage room. The core yard assistants will dispatch the samples with the manifest to the analytical lab. The borehole sample results are used for estimation of ore reserve and for modelling the special distribution of gold in the ore body. Grade control The result from sampling is used for calculating the pay limits for the grades. The results are then taken to the mine planning department which will then decide on which mine grade to mine. The ore reserve estimation The ore reserve estimation process should comply with international legal standards and the grade modelling directly affects the efficiency of underground mining, which has a large impact on the success of the mine. The estimate prepared must be in accordance with the Australasian Code for Reporting of Exploration Results, SAMREC, Mineral Resources and Ore Reserves (“the JORC Code”), provides as follows: Measured Resource: 394,000 tonnes at 10.0 g/t Au Indicated Resource: 620,000 tonnes at 7.1 g/t Au Inferred Resource: 310,000 tonnes at 5.2 g/t Au Total Resource: 1,324,000 tonnes at 4.8. g/t Au Conclusion The core samples are therefore of critical importance and care should be taken to do the logging and especially the sampling as accurately as possible for ore reserve estimations as well. Reference Goldfields South Deep Gold Mine