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Various fluorides were added to a base chromium plating solution to obtain microcracked chromium electrodeposits. Deposition :was done on bright nickel plated mild steel substrates and for most of the experimental work a fresh chromium plating solution was used for each test.The crack counts were statistically anatysed, and in the case of Hull Cell results multiple regression procedures found qU,antitative relationships between crack counts and fluoride concen..t ration together wi th current density. Covering Power, measured with a Hull Cell was quantitatively influenced by both fluoride concentration and the alkali metal part of the molecule. Microcracking only occurred within a relatively narrow range of fluoride concentration and a theory is proposed. Simple compounds such as lithium fluoride did not cause microcracking when plating wa's done In plastic containers but the same solution ,electrolysed in a glass container gave a microcracked deposit. Fluorosilicates caused micro cracking in either glass or plastic containers.. A mechanism is suggested for the formation of reaction prooducts of glass and fluorides, these products being similar to fluorosilicates in that they both cause micro cracking . The alkali metal part of the fluoride molectlle influences microcracking and quantitative relationships were found between microcracking and various parameters of the alkali metal such as atomic number. Caesium is apparently anomalous having a greater effect on microcracking than the other alkali metals. Although 'the type of fluorideiiand the alkali metal part of the fluoride molecule influence microcracking the most important, effect was found to be fluoride concentration. Since fluorides break down during electrolysis even if only slowly it is incorrect to call them catalysts and some experimental evidence has been found for the incorporation of fluorine into the electrodeposit.

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The final gold product of Tau Lekoa mine has a low fineness. This is caused by high concentration of bases metals in the reefs. Some of these base metals together with gold are leached with cyanide and are loaded into carbon. If not adequately controlled, they may elute with gold and contaminate the final product in the electrowinning process. Based on the understanding of the kinetics of the elution, four parameters, namely temperature, flow rate, free caustic soda concentration and cyanide strength, were evaluated first for the elution process. Experimental runs on the plant scale did prove that the first three parameters are the predominant parameters that maintain base metals in the carbon during the elution and therefore assist in the improvement of the fineness of the final product. Recommendations were made to change the operating conditions and the fineness of the gold did improve from 80% to 84 %. In addition, a thermodynamic model that took to consideration the competition of gold and nickel was developed for the electrowinning process. This model showed that the deposition of gold and nickel during the electrowinning was dependant of their concentrations and temperature. The single pass efficiencies and the deposition rates were also tracked during the experimental. Based on the finding on the reduction of electrowinning time, the fineness of the final product was improved from 84% to 85%. As the refining cost depends on the fineness of gold, the improved fineness means that the gold content in the bullion is increased and the impurities are decreased, therefore, the refining cost will decrease as lower penalty costs are charged for the treatment of the bullion with high fineness. The recommendations of the changes have been implemented permanently and these did show permanent improvement of the fineness.

Source: Dissertation Abstracts International, Volume: 33-05, Section: B, page: 2115. / Thesis (Ph.D.)--The Florida State University, 1972.

The Kassandra mining district in Chalkidiki is an important producer of base and precious metals in northern Greece. The mining district is comprised of two major Pb-Zn (Ag [plus or minus] Au) carbonate-replacement deposits at Olympias and Mavres Petres with total mineable reserves of 0.7 Mt Pb, 0.9 Mt Zn, 64 Moz Ag and 4.1 Moz Au. Skouries is a Cu-Au porphyry resource under development with reserves of 3.6 Moz Au and 0.8 Mt Cu. Despite available data, the geodynamic background of the polymetallic district mineralisation is unknown in the context of regional tectono-magmatic evolution. The scope of this PhD project was to develop an over arching ore-genetic model for the diverse mineralisation styles in the Kassandra mining district. The polymetallic zonation and spatial distribution of diverse mineralisation styles in the study area is characteristic for an intrusion-centred ore system. Subeconomic to economically important Cu-Au porphyry copper, Cu-skarn, Pb-Zn (Ag [plus or minus] Au) carbonate-replacement and basement-hosted Fe-Pb ([plus or minus] As) sub-epithermal vein mineralisation between Olympias, Mavres Petres, Madem Lakkos, Stratoni-Fisoka and Skouries represent the proximal to distal parts of a fault-controlled magmatic-hydrothermal system. Fluid inclusion and stable isotope data provided by previous authors identified magmatic and evolved meteoric-hydrothermal fluids in the mineralisation system. New He and S stable isotope data support the involvement of a magmatic component as important metallogenic source for metals, ligands, fluids and heat. Spatially and genetically related to the mineralisation are Oligocene-Miocene stocks and dykes of granite, granodiorite diorite, diorite-gabbro and subordinate gabbro. U-Pb zircon and [sup]40Ar-[sup]39Ar mica ages constrain the mineralisation-related calc-alkaline, medium-K to shoshonitic magmatism to a short-lived cycle between 29 Ma and 20 Ma. A late Oligocene [sup]187Re-[sup]187Os isochron age of 26.1 [plus or minus] 5.3 Ma for ore-related arsenopyrite from the Olympias deposits provides a robust in-situ formation age for the carbonate-replacement mineralisation in the district. Two [sup]40Ar-[sup]39Ar biotite ages of 26.3 [plus or minus] 0.3 Ma and 19.9 [plus or minus] 0.2 Ma date the porphyry-style mineralisation-alteration at Stratoni-Fisoka and the economically important Skouries Cu-Au porphyry resource. Magmatism and magmatic-hydrothermal mineralisation in the district were coeval with a phase of post-collisional extension in the North Aegean region. Eocene-Miocene slab roll-back initiated orogen-scale lithospheric stretching, crustal thinning and asthenospheric upwelling which elevated the regional heat gradient. Heat transmission into lower structural levels of the Rhodope nappe pile started and maintained hydrothermal fluid circulation which led to the formation of base metal rich-deposits. Metamorphic and protolith ages of host and country rocks allocate the district mineralisation to the middle to upper tectono-stratigraphic crustal levels. Here, on the flank of the Southern Rhodope core complex, the heat flux was not high enough to initiate large-scale fluid flow. Instead, synetensional partial melting at mid to lower crustal levels, involving fertile and hydrous cumulates in the subduction-modified sub-continental lithospheric mantle, generated hydrous melts with subduction-type chemical signatures that were emplaced in the Kassandra mining district in the magmatic arc above the retreating slab.