Iran is considered to be the sixth largest consumer of gold in the world, whose producers need gold bullion as a standard material for the production of artifacts. However, because of the shortage of mines and gold reserves, as well as absence of a gold bullion refining center in the country, manufacturers are forced to use melted jewellery scraps as the primary material. On the other hand, analysis of more than 300 pieces of gold alloys using XRF showed that there are three unusual elements of the PGM group, including rhodium, ruthenium and especially iridium in about 30% of them. These elements cannot be detected and/or isolated in gold laboratories using national and international standards (such as cupellation method), and hence the gold karat is incorrectly determined higher than its actual amount, which confuses operators of cupellation labs and makes systematic errors in the test results. Moreover, it is economically important to detect and quantify the PGMs content in gold alloys because of their lower price than gold. Therefore, one of the aims of this thesis is to find simple, inexpensive and accessible methods for the detection of the PGMs, especially iridium (since most jewellery scraps containing this element), during the conventional gold tests. Therefore, it was investigated the effects of the PGMs in gold alloys both on its assay during the cupellation process and on its appearance and microstructural transformations using scanning electron microscopy (SEM), energy-dispersive electron spectroscopy (EDS), X-ray diffraction (XRD), and X-ray fluorescence (XRF) techniques. Visual iection revealed that the upper surface of PGMs-containing beads is typically matte and coarse with black rough cavities of an irregular oval-like shape. Also, the observation of dark spots and lines on just one side of rolled beads, as well as blister-like appendages on the parted and annealed cornets, were found to signify the presence of the PGMs in the gold alloys. XRF analysis along the vertical section of the beads indicated that the amount of the PGMs is not same at different parts of the beads. After the parting and annealing steps, the PGMs form cubic-like structures surrounded by fcc gold sponge-like structures. As a consequence, both visual and microstructural examination of gold alloys during the cupellation process might be used as simple and useful strategies to identify the presence of the PGMs in gold alloys to prevent incorrect karat reports. Since it is necessary to make the final golden cornets without the PGMs, in the next section, different methods used for the gold separation from impurities and PGM were studied and compared. Considering the advantages and disadvantages of the existing methods for the extraction of gold, the method of dissolving the parted cornets in aqua regia and then selective precipitation of gold using SO2 gas as the best reducing agent was selected. To omit gold loss, aqueous solution of SO2 gas (produced by the reaction of sodium metabisulfite with sulfuric acid) was used instead of direct SO2 gas blowing. The gold amount in alloys containing PGMs was determined using the suggested strategy with high accuracy and precision. A gold recovery as high as 99.7% with enough big grain size and high purity (99.9%) was obtained. The obtained karat was comparable with the other methods, such as the National Standard Method and XRF. The proposed method was also used for the extraction of gold from its alloys in a larger scale to produce gold ingots in the Muteh gold mine, which was approved with acceptable economic efficiency. The results of this thesis were used to the revision and amendment of the National Standard of Iran No. 8106 and the International Standard ISO11426 and are also applicable in gold laboratories for the gold test as well as in gold workshops for the ingots production.