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ChalkMine extracts a very hard fine grained olivine basalt from its quarry at Junction View 40 kilometres south of Gatton in south-east Queensland. As part of its obligation to the the Department of Transport and Main Roads when assessing the quarry for re-Certification, a petrological examination of the basalt is required from the current quarry face. The petrological report assesses the durability, hardness and over-all rock quality and gives an in-sight into the over-all quality of the aggregates and road bases that are produced from this rock.
The fine grained nature of the basalt is due to the fact that is derived from a lava that cooled quite quickly as it flowed from its original vent. Normally the finer the basalt the harder it is. The Californian Bearing Ratio (CBR value) is a penetration test for the evaluation of the mechanical strength of road subgrades and base coarses
The CBR rating was developed for measuring the load-bearing capacity of soils used for building roads. The CBR can also be used for measuring the load-bearing capacity of unimproved airstrips or for soils under paved airstrips. The harder the surface, the higher the CBR rating. A CBR of 3 equates to tilled farmland, a CBR of 4.75 equates to turf or moist clay, while moist sand may have a CBR of 10. High quality crushed rock has a CBR over 80. The standard material for this test is crushed California limestone which has a value of 100. The ChalkMine highest quality road base (called a type 2.1) is currently 140 which is quite impressive. Many competitor quarries have their source basalt derived from within the vent itself and consequently the basalt has cooled more slowly and the resultant basalt is coarser grained. The grain size impacts on the hardness and durability of the end product.
These reports below are prepared by Geochempet Services they are petrological and geochemical consultants