Characterisation of in situ gold particle size and distribution for sampling protocol optimisation
- Authors: Dominy, Simon , Xie, Y. , Platten, Ian
- Date: 2008
- Type: Text , Conference proceedings
- Full Text: false
- Description: Sampling protocols that are designed to suit the mineralisation style will result in a reduction of the nugget effect and hence resource risk. The a priori need for all sampling programs is the effective characterisation of the mineralisation type(s) to support optimisation. This requires a program of sampling for sampling followed by holistic characterisation. At each end of the coarse-gold to fine-gold spectrum, the samplability of a deposit ranges from relatively simple for fine-grained disseminated gold particles, through to extremely difficult for coarse nuggety mineralisation. Many deposits contain a proportion of both particle size types. The proportion and size of coarse gold particles has a direct impact on the effectiveness of sampling, where coarser particles will require larger samples and more specialised protocols. The nature of mineralisation geology/mineralogy and associated gold particle sizing can only be determined by sampling to facilitate optimised protocols. Mineralogical studies, focusing on particle size, particle clustering and distribution in host minerals, are required as part of wider paragenetic and metallurgical investigations. This paper discusses the role of mineralogical studies in the characterisation of gold ores for sampling optimisation through a series of case studies.
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.
Mineralogical domains within gold provinces
- Authors: Hughes, Martin , Phillips, Neil
- Date: 2015
- Type: Text , Journal article
- Relation: Transactions of the Institutions of Mining and Metallurgy, Section B: Applied Earth Science Vol. 124, no. 3 (2015), p. 191-204
- Full Text: false
- Reviewed:
- Description: Mineralogical domains use hypogene minerals (i.e. minerals not modified by weathering) and related geochemical characteristics of mineral occurrences, not only ore deposits, to subdivide large mineralised regions. Their use in the Victorian gold province is described using readily available historical data and field checking, and this is a scheme that has not required modification since 1997.The Victorian province is typical of sediment-hosted hydrothermal ores in metamorphic terrains (often termed orogenic gold deposits). Five distinctly different mineral assemblages are used to subdivide all Victorian gold occurrences into eight domains up to hundreds of kilometres in length and tens of kilometres in width. These parallel the regional structural trend and most are closely associated with, or sharply bounded by, major regional-scale faults. Seismic work has shown these faults to be listric thrusts, which flatten into a zone of duplexed greenstones overlying older basement rocks in the deeper crust. Although not defined genetically or temporally, mineralogical domains provide an additional variable related to fluid flow to assist genetic interpretation such as the scale at which a combination of processes operates, permitting predictions as to the origin of the fluids and their pathways. The variations in mineralogy in Victorian gold occurrences indicate that ore fluid compositions differed significantly between adjacent domains, and between areas overlying different regions of deeper crust. The pattern of domains gives clues to the existence of multiple mineralising events and to the degree of overprinting of these events. Domains also assist genetic comparisons by projection into similar adjoining regions to create new domains, for example Tasmania (Mathinna domain and Lefroy sub-domain), NSW (Cobar domain) and New Zealand (Reefton domain). The domainal pattern has application to mineral exploration, metallurgy and environmental issues. Mineralogical domains could be applied elsewhere, particularly in the study of difficult-to-subdivide sedimenthosted gold ores and Archaean greenstone-hosted gold, and possibly for other commodities, especially those that occur as hydrothermal ores. © 2015 Institute of Materials, Minerals and Mining and The AusIMM.