Validation of reverse circulation drilling rig for reconciliation purposes

Abstract

Representative samples of ore containing precious metals is a difficult task. The lower the grade and the higher the nugget and/or cluster effect, the more complex and difficult extracting samples that are both accurate and precise. Reconciliation practices can be used as an effective tool to evaluate sampling accuracy throughout grade control processes. However, a proper reconciliation system must be based on reliable data and, therefore, optimisation of sampling techniques is a must for development of a reliable reconciliation system. This paper is a result of an extensive reconciliation study carried out at a copper and gold mine in Brazil, where a significant reconciliation problem took place while using manual sampling for grade control and short-term modeling. After analysing several sampling equipment/sample selection techniques, the authors suggested the use of a reverse circulation drilling rig with an automatic sampling system for grade control sampling. The samples generated by this automatic system were compared with the manual samples collected from the piles generated by the previous percussion rotary air blast drilling rig. Also, three pairs of twin holes were drilled in order to validate the new reverse circulation approach. Results allowed estimation of the bias related to the increment weighting error (IWE) generated by manual sampling, and show that the reverse circulation rig eliminates significant sampling biases, thus improving the general sample representativeness by increasing both sample accuracy and precision.

Evaluation of Coarse Gold-Bearing Conglomerate Mineralisation at Beatons Creek, Pilbara, Western Australia: Sampling for Resource Development and Grade Control

“…The cyclone feed-to-bag process is also not devoid of sampling errors [5,37,50]. Recovery of the A and B samples at the rig was via a static cyclone/fixed cone splitter attached to the side of the rig or trailer-mounted (Figure 7).…”

“…In coarse gold mineralisation, RC drilling provides both advantages and disadvantages compared to diamond core drilling [37,50]. Key positives include the fact that the mass of the primary sample is larger by generally one order of magnitude (e.g., NQ to PQ core, 5.5-15.5 kg/m versus 5-5.5 ′′ RC, 34-41 kg/m) and that any gold particle clusters are destroyed, and the gold particles are redistributed in the sample.…”

Importance of good sampling practice throughout the gold mine value chain

“…More recently, BH has been replaced with reverse circulation (RC) drilling in an attempt to improve sample quality and grade control outputs (Pitard 2008;Chieregati, El Hajj, Imoto and Pignatari 2015).…”

“…In many open pit gold projects, blast hole (BH) drilling has been used as the principal grade control sampling method. More recently, BH has been replaced with reverse circulation (RC) drilling in an attempt to improve sample quality and grade control outputs (Pitard 2008;Chieregati, El Hajj, Imoto and Pignatari 2015).…”

Optimal grade control sampling practice in open-pit mining – a full-scale blast hole versus reverse circulation variographic experiment

“…According to Pitard (2008), Magri et al (2011) and Chieregati et al (2015), RC sampling gives more reliable results than BH sampling. It is argued that reduced sampling error effects justify the higher drilling costs for RC.…”