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Lihir achieved the target of an annualised 15mtpa sustainable mill throughput rate in the June 2019 quarter. Having achieved this target, Lihir is looking to stabilise throughput at or slightly above these levels and increase focus on lifting recovery rates to maximise overall gold production and cash flow in the future.
The board endorsed the progression to Feasibility Study with respect to a near shore cut-off wall in place of a coffer dam, substantially reducing expected future capital expenditure on the seepage barrier.
Newcrest creates economic value for PNG and local communities including direct revenues from operations, investments in public infrastructure and services, support of local suppliers and a range of indirect economic benefits.
We also contribute to the local economy in accordance with agreements with the government and landowners by providing public infrastructure and services, including access to health services and the provision of electrical power and water to local villages.
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A 2015 study by Minerals.org.au revealed Australias gold reserves to be more than 16% of global gold reserves around 9,500 tonnes. Also possessing the biggest share of economic gold reserves in the world, Australia stands as a major contributor to global gold trade.
Australia is ranked second-largest gold producer in the world behind China, with the period 2015-16 seeing 282 tonnes of the precious metal produced the countrys highest yield in 13 years. Gold is the countrys third-largest mineral export in terms of earnings.
Around 75 mining operations in Australia have their primary output as gold, with many mining from both open-cut and underground operations, while producing gold resources from more than two deposits. Additionally, many non-gold mining operations produce gold as a by-product.
Newcrest Mining Limited headquartered in Melbourne, Victoria tops this list. The fourth-largest mining company in Australia, Newcrests operations started in 1996. Its mines are located in Australia, Papua New Guinea, Indonesia and the Ivory Coast in Africa.
In 1992, Newcrest discovered the Cadia Hill orebody near the city of Orange, New South Wales. After commercial production began in 1999, Cadia became one of Australias largest gold mining operations and now boasts a production of more than nine million troy ounces of gold. Another Newcrest mine at Telfer, in Western Australias Great Sandy Desert, generates annual gold production of about 500,000 troy ounces.
Backed by strong reserves and resources, Newcrest Minings business success chiefly runs on a portfolio of seemingly inexhaustible, yet inexpensive mines helped by a selection of greenfield and brownfield exploration projects. Newcrest produced 76.4 tonnes of gold in 2018.
Starting with a single mine and an annual gold production of 100,000 troy ounces in 2010, Northern Star has risen in stature to currently operate five gold mines producing about 525,000 to 575,000 troy ounces of gold annually. These five mines Kundana, Jundee, Plutonic, Kanowna Belle and Paulsens have together produced more than 20 million troy ounces of gold.
Headquartered in Perth, gold mining specialist Evolution Mining is Australias sixth-biggest mining company and third on our list. Relatively new to the mining industry, with operations starting in 2011, Evolution ranks 49th in the world in this sector.
Evolutions mining operations consist of three in Queensland, one in Western Australia and one in New South Wales. Having a 100% interest in its projects, the gold miners robust portfolio of production and growth has seen it rise to become the second-largest listed gold mining company on the Australian stock exchange.
Another Perth-based gold mining company, Saracen Mineral Holdings Limited has three mines in the neighbourhood of Kalgoorlie, Western Australia. With a current gold production of more than 500,000 troy ounces, new investments in exploration and technology hold a promise of a further increase in production and mine life.
Saracens main gold production is generated by Carosue Dam and its new Thunderbox mine, both of which are in Western Australia. Strong cash flow from Thunderbox and Carosue Dam reflect Saracens position as a company with no debt, better exploration facilities and increasing gold reserves.
Perth-based exploration and gold mining company Regis Resources boasts of successful mid-sized gold operations in not just Australia but also Africa. Purely into gold mining, Regis Resources operations include the McPhillamys Gold Project and the Duketon Gold Project.
The Duketon Gold Project located in Western Australias North Eastern Goldfields is 100% owned by Regis Resources and carries a total annual milling capacity of 10 million tonnes. Its operations began in mid-2010 after the Moolart Well Gold Mine was constructed. After acquiring the Gloster Gold Deposit in 2015 along with other surrounding minor deposits, Regis began to blend ore with a reasonable amount of success in a bid to extend the Projects mine life.
The McPhillamys Gold Project was acquired by Regis in late 2012 from Newmont Exploration and Alkane Resources. Located in New South Wales Central Western region, McPhillamys embodies Regiss future growth in the sector.
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BjrkdalThe Bjrkdal gold deposit is a lode-style, sheeted vein deposit hosted within the upper portions of the Skellefte Group sediments. Gold is found within quartz veins that range in thickness from less than a centimetre to over several decimetres. These veins are usually observed as vertical to sub-vertical dipping veins that strike between azimuth 000 and azimuth 090, with the majority of veins striking between azimuth 030 and 060. The veining is locally structurally complex, with many cross-veining features observed and thin mineralized quartz veinlets in the wall rocks proximal to the main quartz veins.Gold-rich quartz veins are most often associated with the presence of minor quantities of sulphide minerals such as pyrite, pyrrhotite, marcasite, and chalcopyrite alongside more common non-sulphide minerals such as actinolite, tourmaline, and biotite. Scheelite and bismuth-telluride compounds are also commonly found within the gold-rich quartz veins and are both excellent indicators of gold mineralization. Gold occurs dominantly as free gold, however, gold mineralization is also associated with bismuthtelluride minerals, electrum, and pyroxenes. Silver is seen as a minor by-product of the Bjrkdal processing plant, however, very little is known about its deportment within the deposit, although it is assumed to be associated with electrum.Skarnification occurs commonly within the Mine, especially in the limestone/marble unit where it occurs as discreet patches and lenses. However, similar calc-silicate alteration has taken place in areas where local shearing has affected the volcanoclastic host rock. Shearing is a known mechanism of skarnification. The skarnification here is most likely due to fluid influx where shears and faults interacted with the limestone/marble unit or calcite banded volcanoclastic rocks. The limestone/marble unit is predisposed to accommodate strain and be exploited by structures due to the rheological difference between the limestone/marble and the surrounding volcanic and volcaniclastic rocks.The most striking feature of the Bjrkdal Au system is the anastomosing, sheeted quartz-vein network in which the majority of gold is hosted. This epigenetic vein network appears structurally controlled, consisting of more than a thousand sub-parallel quartz veins (typically striking 030 to 090 from truenorth). Such strong structural-geological influences over geometry of any quartz vein hosted mineralization clearly suggest a strong spatial and temporal relationship with orogenic/tectonic processes (i.e., mesothermal/greenstone gold systems). However, the mineralogical associations with gold mineralization, and the larger alteration signature of the Bjrkdal area, could also suggest that alternative depositional mechanisms are responsible for the mineralization at Bjrkdal as there are some similarities with skarn and/or porphyry systems.The main type of mineralization found in the Bjrkdal gold system is dominated by vertical to sub-vertical dipping quartz-filled veins. Common accessory minerals contained within these veins are (in approximate order of occurrence): tourmaline, calcite, biotite, pyrite, pyrrhotite, actinolite, scheelite, chalcopyrite, bismuth-tellurides (pilsenite and tsumoite), gold, and electrum. Gold mineralization is most closely related to the bismuth-telluride minerals, and is also more reliably encountered in veins with high abundances of pyrrhotite, pyrite, scheelite, and/or chalcopyrite. In general, veins of pure quartz and free of the accessory minerals listed above are generally quite poor hosts for significant quantities of gold mineralization. As such, the informal terminology of clean veins and dirty veins has been adopted at the mine site in order to quickly describe vein-fill characteristics. Structural analysis of these two distinct vein-fill types from the Main Zone -325 and -340 levels suggests that the cleaner veins will more often strike between 030 and 040 from true north, while the dirty, inclusion-rich veins are more likely to strike between 050 and 090 from true north. This structural-geochemical relationship suggests that vein development in the Bjrkdal deposit occurred as more than a single vein-forming event, and that the fluids responsible for the vein-fill and mineralization were evolving with time.NorrbergetThe primary mineralization at Norrberget is observed to be associated with amphibole alteration bands and veinlets, and where mafic tuffs and volcaniclastic rocks are interbedded, contrary to what is observed at Bjrkdal. The mineralization is preferentially emplaced where there is a structural change to the rock such as at lithological contacts, altered bands and where shearing interacts with the interbedded sequences, due to the changing in the rheological characteristics of the unit. Zones where pyrrhotite and pyrite occur and are absent appear to be lithological controlled within the volcaniclastic package which can indicate a differing redox based upon temperature change and fluid evolution.The mineralization at Norrberget is limited spatially to 50 m stratigraphically below the lower marble contact, which is believed to be a result of the cooling and redox changes of the fluid as it passes through the units. The gold is very fine grained and rarely visible. Where gold grains have been observed, they are found to be on the boundary or in the interstitial material between grains. High grade gold is mostly found in areas with low to no pyrite.The major controls on the mineralization at Norrberget include the large scale shear zone that marks the base of the marble unit, the rheological differences between different stratigraphic units, the variation in the lithological and porosity of the volcanic package, and the development of the fluid system which utilized the shear zone. These large scale shear zones run extensively through the area along the base of the marble unit which extends beyond the Mine and across Norrberget. The mineralization occurs principally within a package of heterogeneous volcaniclastics containing interbedded ash falls, flows, and tuffs which have varying composition along with differing porosity and rheological characteristics. Where the Norrberget volcaniclastics are not sheared, they are packaged conformably between metasedimentary rocks and mafic volcanic rocks above and medium grained subvolcanic intrusions and volcanic rocks below.The mineralization at Norrberget is stratabound within an interbedded altered volcaniclastic package that sits unconformably below a 30 m to 40 m thick marble unit. Gold mineralization has been observed up to 50 m below this contact. Gold mineralization is principally hosted in an amphibole-albite banded alteration and is also common where volcaniclastics are interbedded with crystalline tuff units. Theses alteration bands vary between one centimetre and 50 cm in thickness, are typically fine to medium grained, and appear to be sheared. Trace sulphides and minor quartz/carbonate are associated with the bands.
Prior to 2020, production was split between the underground mine and the open pit. In 2019, mining of the open pit was stopped for economic reasons and this production was replaced with ore from the low grade stockpile and an increase in underground production. The remaining open pit material remains economically viable, however, the low grade stockpile realizes more value, so open pit mining has been deferred for several years until the stockpile is run-down and open pit production is needed to offset reducing underground production. The current production strategy is to maximize the underground extraction with the remaining ore coming from stockpiles. Underground production for 2021 is planned to be 960,000 tonnes which is derived from the updated Resource Model and Mineral Reserves. The current 2021 Mining Budget includes additional material and was derived from the previous Resource Model. No production from the open pit is planned in 2021. Instead, 340,000 tonnes of ore will be drawn from the stockpile to make up the balance of the mill feed. As presently envisaged in the LOM plan, open pit pre-stripping and production will be restarted in 2024 to supplement the decrease in production from the underground mine.The open pit has currently been halted and is planned to be restarted in 2024, however this could be delayed further in the event of additional underground reserves being identified. The planned method is standard truck and shovel mining, as done historically. Details will be redefined closer to the restart date.The known Bjrkdal underground deposit lies within a footprint of approximately 1,600 m x 600 m and has a vertical extent of approximately 400 m. The long-term LOM underground production rate is planned to average 975,000 tpa up until 2023, and 775,000 tpa thereafter until production tails off in 2027. On vein development (OVD) will be carried out over approximately three years and stope production will be carried out over approximately seven years. A decrease in production is planned after 2023, when underground output reduces, with the balance being made up with open pit and stockpile tonnes.Primary access to the underground operation is via ramp systems originating from two portals located in the wall of the existing open pit. Open pit mining and removal of the crown pillar in the north/east wall will disrupt this access as well as the supply of other services such as emergency egress, electrical, ventilation, and mine drainage systems. Open pit ore mining will therefore commence at Nylunds initially until underground operations cease, with limited pre-stripping only above the underground access and infrastructure in the crown pillar area.The underground mining method used at the Mine is longhole stoping with a sub-level spacing of 15 m to 20 m, depending on the zone. Cross-cuts are established perpendicular to the vein system. Veins are then developed by drifting on each sub-level from the cross-cut. All pre-production vein, cross-cut, and ramp development is drilled and blasted using conventional trackless mining equipment.Stoping blocks are currently drilled with approximately 15 m long 70 mm diameter up-holes connecting to the bottom of the overlying stope using Epiroc Simba drill rigs. When production drilling is completed, initial slot raises are developed and drill lines blasted in groups of three to five rings using a burden of 1.5 m and retreating towards the hanging wall. The material is removed between blasts, which also allows a void for the following blast.The objective of the current materials handling strategy is as follows: Development material from cross-cuts and ramps above a grade of 0.32 g/t Au is hauled to a Bore stockpile at the mill. OVD material is either hauled to the OVD production ROM stockpile where it is classified as waste or ore and sent to the appropriate location. All stope production, regardless of grade, is hauled to the stope production stockpile.In consideration of the variable vein geometry and existing equipment configuration, 3.5 m has been measured as the average minimum mining width. This includes a base 2.5 m minimum width plus an allowance for 0.5 m of overbreak on both the hanging wall and footwall sides of the stope. An additional 10% dilution is added for planning purposes.Most of the mined out stopes are left open without any backfill, however the relatively new Aurora Zone will have stopes that will be both wider, longer, and higher than in other areas. In these areas, the stopes are planned to be mined and backfilled with unconsolidated fill. This will allow pillars to be reduced and will increase the extraction ratio.
Ore is delivered to a series of small stockpiles that are utilized to campaign ore through the processing facility in order to provide reconciliation data for various parts of the mines. From the stockpiles, a frontend loader feeds a jaw crusher. Discharge from the jaw crusher is screened. The screen undersize is nominally minus 8 mm. The material is conveyed to a 5,000-tonne fine ore bin or to an emergency stockpile. Screen oversize is stored in a 400-tonne stockpile. Ore is reclaimed from the stockpile and fed to a secondary cone crusher. Discharge from the cone crusher is conveyed to a second screen. Undersize from the screen is combined with the undersize from the first screen and stored in the fine ore bin or the emergency stockpile. Oversize from the second screen is fed to a tertiary cone crusher. The discharge from the tertiary crusher is combined with the discharge from the secondary cone crusher and fed to the second screen. Thus, the ore is recirculated through the tertiary cone crusher until it meets required product size (i.e., minus 8 mm).Crushed ore is reclaimed from the fine ore bin and passed across a series of two screens prior to being fed to the primary grinding circuit. The screen oversize is directed to an oversize material stockpile. The screen undersize is split and fed to the primary ball mill and primary rod mill that are operated in parallel. Discharge from the primary mills is fed to a classifying screen. The screen oversize is returned to the primary ball mill for additional grinding. Screen undersize has a particle size of approximately 80% passing (P80) 560 m. The slurry is pumped to hydrocyclones for additional classification.
The concentrator includes primary, secondary, and tertiary crushing, primary, and secondary grinding, a series of gravity concentration steps, regrinding, and flotation to produce three gravity concentrates and a flotation concentrate.The cyclone underflow (P80 800 m) is fed to rougher spiral concentrators. Tailings from the rougher and cleaner spirals are returned to the secondary ball mill number 3 with a discharge P80 475 m. From the discharge of mill number 3, the slurry is pumped to combine with the discharge from ball mills 1 and 2. The discharge from the three mills is pumped to the classifying screen. Concentrate from the rougher spirals is fed to the cleaner spiral classifiers. Tailings from the cleaner spirals are combined with the tailings from the rougher spirals and processed in the regrind secondary ball mill number 3 circuit. Concentrate from the cleaner spirals is cleaned on shaking tables. Tailings from the shaking tables are fed to a Knelson centrifugal ........
This chapter considers comminution for gold ores, starting with breakage induced in the blasting process, continuing through primary crushing, primary milling, and secondary milling. Both technical and operational considerations are reviewed; while gold ore comminution is broadly similar to like-sized circuits for other mineral processing applications, specific considerations applicable to gold circuits are highlighted. Although significant production of gold comes from both heap leaching (including run-of-mine and crush-for-leach) and milling operations, milling operations are present at 18 of the 20 largest producing gold operations in the world. As such, the majority of this chapter targets discussion of milling operations, in particular, the various configurations of primary milling circuits including crushing, autogenous/semiautogenous, and crusher/high-pressure grinding rolls circuits. Further, the capital and operating costs, the complexity of milling operations, and the risk and opportunity from good circuit design and operation merit focusing on milling operations. Elements specific to gold ore processes, such as dry grinding for roasting operations, security considerations for gold milling, reagent additions, and integration of mineral processing steps in the comminution circuit, are also addressed.
John B. Mosher is presently VP-Global Security at Freeport-McMoRan Copper & Gold Inc., before which he was SVP for their Morenci operation, and he also directed the Metallurgy Department at PT Freeport Indonesia. He has extensive experience inthe comminution and beneciation of copper, gold, and lateritic nickel ores. Hehas worked on crushing and grinding circuits in an operational or consulting role in six continents, with a focus on the process development, testing, design, and optimization. As a project manager at Hazen Research, he oversaw laboratory and pilot programs for gold extraction including greenelds project development, plant expansions, recovery improvement programs, and process optimization. He holds an MS from the Colorado School of Mines and a BS from the United States Military Academy.