Gold particle clustering : A new consideration in sampling applications
- Authors: Dominy, Simon , Platten, Ian
- Date: 2007
- Type: Text , Journal article
- Relation: Transactions of the Institutions of Mining and Metallurgy, Section B: Applied Earth Science Vol. 116, no. 3 (2007), p. 130-142
- Full Text: false
- Reviewed:
- Description: Recent research indicates that an enhanced coarse gold problem may be present in some gold deposits. This can be due to the presence of gold particle clusters that give the effect of individual coarse-gold particles and leads to a high constitution heterogeneity (CH). These clusters, which may be distributed on the centimetre-scale or greater, give rise to high assay variability in field samples. However, once a sub-sample is pulverised, the effect of the clusters may be removed if the individual gold particles making up the clusters are liberated. Thus any resulting pulp will tend to have a low variability, unless true coarse-gold particles exist. Clusters are readily recognised in coarse gold deposits where they accentuate existing high nugget effect and CH. Clusters may however also occur in fine gold deposits where they produce an apparent coarse gold style. This is signaled by an unexpectedly high nugget effect from variography and poor correlation between field sample duplicates. The Gy sampling equation is applied to model coarse and fine gold deposits with clustered and non-clustered gold grains. Case studies illustrating observed effects of clustering are presented. If clustered particles exist, then proper protocol design at the field and early laboratory stage is paramount. The sample characterisation stage should include an assessment of possible gold article clustering, in addition to the standard descriptions of the gold particle size distribution. © 2007 Institute of Materials, Minerals and Mining and The AusIMM.
- Description: C1
- Description: 2003005555
Grab sampling for underground gold mine grade control
- Authors: Dominy, Simon
- Date: 2010
- Type: Text , Journal article
- Relation: Journal of The South African Institute of Mining and Metallurgy Vol. 110, no. 6 (2010), p. 277-287
- Full Text:
- Reviewed:
- Description: Geologists in some underground gold mines collect grab samples from broken ore piles or trucks as a method of grade control. It is often known as muck sampling. Generally, the goal of grab sampling is to try and reconcile the mined grade at the ore source to the predicted grade and/or predict the mill feed grade. The mass of the sample collected is limited by health and safety issues, as well as by the capacity of the laboratory to process the samples within a given time frame. In general terms, grab sampling is known to be problematic because samplers tend to oversample the fines, and/or pick out high-grade fragments; surface sampling of piles does not test material within the pile; muck piles in development drives/faces are likely to be zoned due to the blasting sequence; high or lowgrade material may preferentially segregate in the pile during mucking; the five per cent mass reject size of the material in muck piles is very large from underground blasting; some correlation usually exists whereby the larger fragments are enriched or depleted in the critical component of value; and the average error made in estimating the true stockpile grade is likely to be high. The method is prone to chronic fundamental sampling, grouping and segregation, delimitation, and extraction errors. Substantial warnings must be given about the use of grab sampling for grade control in gold mines. The method may appear to work sometimes, which can be attributed to a fine gold particle sizing and more disseminated distribution. As with all sampling methods, its appropriateness must be determined by ore characterization and heterogeneity testing to ensure the method suits the ore type. © The Southern African Institute of Mining and Metallurgy, 2010.
Grade control geological mapping in underground gold vein operations
- Authors: Dominy, Simon , Platten, Ian
- Date: 2012
- Type: Text , Journal article
- Relation: Transactions of the Institutions of Mining and Metallurgy, Section B : Applied Earth Science Vol. 121, no. 2 (2012), p. 96-103
- Full Text: false
- Reviewed:
- Description: Grade control is a process of maximising value and reducing risk. It requires the delivery of tonnes at an optimum grade to the mill, via the accurate definition of ore and waste. It essentially comprises data collection, integration and interpretation, local resource estimation, stope design, supervision of mining and stockpile management. The foundation of all grade control programmes should be that of geological understanding led by clear and accurate mapping and representative sampling to drive appropriate estimation strategies and mining. Gold veins show features relating to erratic grade distribution (nugget effect), and variable geometry and internal architecture. These features include variations in dip, strike and width, late-stage faulting/shearing effects and vein continuity and type. Variations generally require close geological understanding to ensure optimum grade, minimal dilution and maximum mining recovery. A welldesigned grade control programme will prove to management and stakeholders that by applying geological knowledge, the mining process can be both efficient and cost effective. © 2012 Institute of Materials, Minerals and Mining and The AusIMM.
- Description: 2003010686
Approaches to reporting grade uncertainty in high nugget gold veins
- Authors: Dominy, Simon , Edgar, W.
- Date: 2012
- Type: Text , Journal article
- Relation: Transactions of the Institutions of Mining and Metallurgy, Section B : Applied Earth Science Vol. 121, no. 1 (2012), p. 29-42
- Full Text: false
- Reviewed:
- Description: High nugget effect gold veins are generally considered to be one of the most challenging of deposit types to evaluate and exploit. To potential investors and mining companies, they are viewed as high risk because of the associated uncertainties in the grade estimate and general paucity of reserves at production start-up. Despite the well-known risks, these deposits are often high grade and have a grade upside which makes them potentially attractive. The reporting of resource grade is of importance and perhaps even more so is the reporting of the associated uncertainty attached to the grade estimate. The quoting of the estimated grade within a grade range is recommended to achieve more complete and useful disclosure. The definition of the grade range can be somewhat subjective, ranging from opinion-based through to data-based estimates and geostatistical conditional simulation. Whichever approach is used, the over-riding issue must be the provision of enough data of appropriate quality and full disclosure to the public of relevant uncertainties. © 2012 Institute of Materials, Minerals and Mining and The AusIMM.
- Description: 2003010578
Gold mineralisation and ore controls at the Clogau mine, Dolgellau, north Wales, United Kingdom
- Authors: Dominy, Simon , Platten, Ian
- Date: 2012
- Type: Text , Journal article
- Relation: Transactions of the Institutions of Mining and Metallurgy, Section B : Applied Earth Science Vol. 121, no. 1 (2012), p. 12-28
- Full Text: false
- Reviewed:
- Description: At a recorded production of 2·5 t Au and mill recovered grade of 17 g/t Au, Clogau is the largest and richest mine in the Dolgellau gold-belt and is the most prolific gold producer in the United Kingdom. The main period of production commenced in 1861 and ended in 1911, with intermittent production between 1983 and 2007. The principal gold-quartz bearing Main reef can be traced for about 3 km along strike, trending approximately NE-SW and dipping between 60uSE and 90uSE. The reef system pinches and swells, changes strike, and splits into a number of major and minor branches. Reef width is variable, ranging from 6 m to a few centimetres. The reef is internally complex and composed of swarms of narrow sub-parallel quartz veins separated by sheets of country rock. The gold-bearing vein segments within the composite reef package are discontinuous, though may locally possess bonanza grades running at 1000s g/t Au. The predictability of the gold-rich segments is poor, but has been shown to be related to presence of the Clogau Formation (black-shale), interactions of the reef fault with greenstone sills, and/or reef splitting to form discrete ore shoots. © 2012 Institute of Materials, Minerals and Mining and The AusIMM.
- Description: 2003010576
Continuous carbonatitic melt-fluid evolution of a REE mineralization system : Evidence from inclusions in the Maoniuping REE Deposit, Western Sichuan, China
- Authors: Xie, Yuling , Hou, Zengqian , Yin, Shuping , Dominy, Simon , Xu, Jiuhua , Tian, Shihong , Xu, Wenyi
- Date: 2009
- Type: Text , Journal article
- Relation: Ore Geology Reviews Vol. 36, no. 1-3 (2009), p. 90-105
- Full Text:
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- Description: The Maoniuping REE deposit is a world-class deposit with 1.2 Mt of REO grading on average 2.89 wt.% REO. It is the largest in the 270-km long Mianning-Dechang REE belt and is associated with Himalayan carbonatite-alkalic complexes in the eastern Indo-Asian collisional zone, Western Sichuan Province, China. The deposit is hosted by nordmarkite stocks and carbonatite sills that display a radiometric age of 40 to 24 Ma and which intruded a Yanshanian granite pluton. The 40.3 to 27.8 Ma REE mineralization occurs as vein systems hosted in nordmarkite and carbonatite with minor altered granite and rhyolite. Four ore types are recognized based on ore texture and mineral assemblage: (1) disseminated; (2) pegmatitic; (3) brecciated; and 4) stockwork (stringer) types. Five mineralizing stages are confirmed according to vein crosscutting relationships, mineral assemblage and microthermometric results, these are: 1) carbonatite stage, 2) pegmatite stage, 3) barite-bastnaesite stage, 4) later calcite stage and 5) epigenetic oxidation stage. Varied inclusion assemblages are found in fluorite, quartz, bastnaesite, barite and calcite from stages 1 through to stage 4. The dominant inclusion types include: melt, melt-fluid, CO2-rich fluid and aqueous-rich fluid inclusions. Fluid, melt-fluid and melt inclusion studies indicate that the ore-forming fluid resulted from the unmixing of carbonatite melt and carbonatitic fluid. Initial ore-forming fluids were high-temperature (600 to 850 degrees C), high-pressure (>350 MPa) and high-density supercritical orthomagmatic fluids, characterized by SO4-rich and multicomponent composition (e.g. K, Na, Ca, Ba, Sr and REE). The dominant anion is not Cl. but SO4. The evolution of the ore-forming fluid is from a melt-fluid at high temperature, through a CO2-rich fluid at high to medium temperature to aqueous-rich fluid at low temperature. REE precipitation occurred from a high to medium temperature CO2-rich fluid. The main mechanism for REE precipitation was phase separation of CO2 and aqueous fluids resulting in a decrease of temperature and pressure. (C) 2008 Elsevier B.V. All rights reserved.