Applied Earth Science: Transactions of the Institutions of Mining and Metallurgy

The Rockliden Zn–Cu volcanic-hosted massive sulphide deposit is located approximately 150 km south of the Skellefte ore district, north-central Sweden. Most of the mineralisation is found at the altered stratigraphic top of the felsic volcanic rocks, which are intercalated in the metamorphosed siliciclastic sedimentary rocks of the Bothnian Basin. Mafic dykes cross-cut all lithological units, including the massive sulphides, at the Rockliden deposit. The relatively high Sb grade of some parts of the mineralisation results in challenges in handling of the Cu–Pb concentrate in the smelting process. The aim of this study is to characterise different host rock units and ore types by their main mineralogy, as well as by their trace mineralogy with focus on the Sb-bearing minerals. Ore types are distinguished largely on the basis of their main base-metal bearing sulphide minerals, which are chalcopyrite and sphalerite. Several Sb-bearing minerals are documented and differences in the trace mineralogy between rock and ore types are highlighted. Based on the qualitative ore characterisation, rock- and ore-intrinsic parameters, such as the pyrite, pyrrhotite and magnetite content of the massive sulphides, the trace mineralogy and its association with base-metal sulphide minerals, are outlined and discussed in terms of relevance to the ore processing.

To assess common factors and the key exploration methods in gold discovery we analyse 154 case studies of successful gold exploration. Our aim is to highlight what may help find gold in the future. The case studies used here are only those documented in the consistent series of biennial volumes of New Generation Gold from 1995 to 2013. Surface and near surface sampling dominate early phases of exploration. Subsequently, as a second and third priority drilling, initially rotary air blast or air-core and then reverse circulation and diamond core drilling dominate exploration. The priority order of methods is more or less the order of access from surface. However, some discoveries document reverse circulation or diamond core drilling as the first and primary method suggesting success by bold targeting and early drilling. Gold has no direct recognisable geophysical signature but geophysics is used as an indirect tool to model the geology and weathering. Geophysical methods, be they magnetic or electrical methods, maintain a similar level of interest throughout programmes. Alteration science is recorded as a method in only 13% of discoveries, a comment that may seem at odds with the modern focus on hyperspectral mapping and logging. Similarly and despite being unambiguously the principal control on gold mineralisation, structure is recorded as of use in only 53% of discoveries, usually a 3rd or 4th priority. Of the case studies, 16% make no mention of structure at all. It is surprising that when surface outcrop is available, structural geology is rarely documented as an exploration method. The low levels of reporting of the intellectual activities of alteration and structural geology (and to a lesser extent mapping and geophysics) suggests they are (i) under-reported or, (ii) that current science is inadequate (this is unlikely) or, (iii) they are under-utilised. If under-reported, are the senior managers and directors who wrote these papers aware of the intellectual effort of their teams? Alternatively if under-used, alteration and structure may represent a significant opportunity for the next generation of exploration.

Myanmar contains important deposits of tin, tungsten, copper, gold, gemstones, zinc, lead, nickel and silver. It has one of the most diverse and richly endowed collections of natural resources in Southeast Asia, largely reflecting a geological history stretching from the Late Triassic to the Miocene. At least three world class deposits include Bawdwin (lead–zinc–silver), Monywa (copper) and Mawchi (tin–tungsten). Myanmar can be divided into three principal metallotects: the Wuntho-Popa Arc, comprising subduction-related granites with associated porphyry-type copper-gold and epithermal gold mineralisation; the Mogok-Mandalay-Mergui Belt hosting both significant tin–tungsten mineralisation associated with crustal melt granites, and key orogenic gold resources; and the Shan Plateau with massive sulphide-type lead–zinc deposits. Myanmar as a jurisdiction remains poorly understood and underdeveloped with regards its natural resources. We have built a Geographic Information System database of known Myanmar deposits, outcrops and mineral occurrences as a tool for exploration targeting.

Simulation modelling is a practice commonly used in the mining industry to evaluate alternative process designs. Such modelling is typically undertaken as an optimisation study to increase the efficiencies, productivity and product quality of operating mines. In this situation real short-term grade variability data of extracted ore are available from production records as input data into the simulation. There is also a need for simulation modelling to be performed before mines are approved for construction to clarify the grade variability characteristics that can be expected from the operating mine and assist in the optimisation of the process design. In this situation no historical short-term grade variability data are available. To achieve meaningful and reliable results from a simulation it is necessary to have input data for the ore to be extracted from the pits, representative of the short-term grade variability that would be expected for the operating mine. This paper describes an example of a path taken to generate realistic input data. A method described as composite cut-off criterion was used to distinguish ore from waste which gave substantially greater recovered tonnage at target grade compared to the conventional quadrant cut-off grade criteria. The only data available for the project was resource model data in the form of kriged block models, which are known to underestimate true ore grade variability. To achieve realistic results from the simulation it was essential to increase this variability while maintaining the accurate average grades. Areas of certain deposits that were modelled using both kriging and conditional simulation estimation techniques were quantitatively compared to establish the comparative variance and the kriged data was modified to match the conditionally simulated variance. A realistic mining model was generated via a process of discretisation and regularisation of the resource blocks. Quantitative assessment demonstrated that this method adequately compensated for ore dilution and that adjustment for ore loss was not required due to an ore skin surrounding the edge blocks. The conditioned data were then used to generate a schedule of daily mine extraction, considering grade variability, tonnage, equipment constraints and extensive blended-in-blended-out pre-crusher stockpiles to feed into the process design simulations. For the pre-crusher stockpiles a number of alternative allocation criteria were examined for ore being extracted from the pits to identify the best method in achieving reduced variability through the daily scheduling system. The study concluded that a single analyte separation criterion produced acceptable variability with minimal complexity. The blending efficiency of manually stacked and reclaimed pre-crusher stockpiles was studied to determine a realistic blending efficiency within the pile. A recommended method of building and reclaiming was determined to give maximum blending efficiency. Finally, the data were used as input into process design simulation models; simulation from crusher feed to ship loading demonstrated that control of shipment grade variability was achievable and that the conditioning of the data delivered realistic results.

This paper summarises the technologies available in exploration and mining and describes techniques of core orientation, marking-up, structure measurement and the visual representation of structural data. We provide a critical comparison of tools and methods available at each stage of the process.