Dolomites of White Rock deposit

Abstract

The dolomites of White Rock deposit were explored in 1958. Their composition includes fluxing limestones and dolomites.During use of the deposit disagreement of the data of exploration and actual results, which made it necessary to conduct work on further investigation of the dolomites, occurred.For the purpose of a composite investigation of the raw material the limestones and the dolomitic limestones with not more than 5 wt.% of MgO were evaluated as a metallurgical flux and the dolomites as refractory raw materials.Nine samples of dolomites taken from drilled cores were investigated.In appearance, all of the samples were uniform and light gray in color and the macrostructure of the samples was dense and fine-grained.Under the microscope it may be seen that the structure of the dolomites is mixed grain size (Fig. i). The main portion of the dolomite has a structure from coarse-grained (grain size 0.48-0.80 mm) to very fine-grained (0.04-0.08 mm).Calcite and iron hyroxides with an insignificant quantity of clay material are distributed in "healed" microcracks or in the form of individual inclusions.The presence of calcite in the medium, fine, and very-finegrained varieties of dolomite was established after diagnostic etching in 10% HCI (Fig. ibd).The quantity of calcite in the dolomites of White Rock deposit is from 5 to 16 vol.% and therefore they are considered low-lime ones.The strength properties of the dolomites were studied.The content of the individual fractions obtained after crushing of the material in a jaw crusher and separation into the 20-5, 5-1, and finer than i-mm fractions was taken as the criterion of evaluation of the strength of the dolomites.The data obtained indicates that the investigated dolomites have primarily similar strength, with the exception of samples No. 2 and 3 ( Table i). The increased content in these samples of the finer than l-mm fraction is apparently caused by the more core-grained structure.The average open porosity was from 1.5 to 7.2%, the apparent density from 2.60 tQ 2.77 g/cm 3, and the water content from 0.6 to 2.8%.For all the samples thermogravimetric analysis established two endothermic effects characteristic of the dolomite rocks. The endothermic effects at 770 to 790~ are caused by decomposition of dolomite into MgCO3 and CaC03 and at the moment of its formation the MgCO3 dissociates into MgO and CO2. The amount and temperature of this effect depend upon the size of the dolomite crystals, the degree of isomorphous substitutions and the mechanical impurities~ TABLE io Grain-Size Composition of the Dolomites after Crushing in a Jaw Crusher sample Noo .Wt. ~oof the fraction, mm 20---5 5--1