Gold exploration samples have significant importance in the financial analysis of the project due to give approximate grade and tonnage reserve estimates. Due to the natural variation in mineralization, a cutoff grade must be determined and an average grade at that cutoff is calculated. This is an estimated gold ore reserve because both the average gold grade of the deposit and cutoff grade economically appropriate are needed to evaluate the deposit. Financial analyses contribute to decisions affecting the discovery of a gold deposit or termination of interest.
One method consists of considering variable grade cutoffs, calculating the associated tonnages and average gold grades, and then determining the minimum economic tonnage requirement at each average grade. For example, a cutoff of 0.5 g/t may be used to evaluate the gold deposit potential during the drilling program. Arbitrary cutoffs, either too high or too low could indicate that the deposit is not sufficient profitable to be of further interest. This consideration is important when the deposit is marginal by the company´s criterion, sine it prevents undue emphasis on a standard cutoff grade.
It is important to mention that the most important hand samples and drill cores always wind up in the assay lab. The process that indicates the precise content of rocks is known as assaying. The laboratory chooses an appropriate method to determination the concentration of gold, silver and other metals. The typical method is fire assaying, which consists in melting the sample and the gold and silver content is determined. Other method is wet assaying, which consists in dissolving the samples and metals are recovered using chemical reagents. Once gold assay results are available, the location of the samples and their corresponding assay values are plotted on a map to gives an idea about the distribution of gold and the potential of the deposit. When the gold values are extremely high and the others are very different, the high values must be studied carefully due to these assays may not reflect the gold grade around the sample point location.
If the gold assay results come from channel samples or drill cores, they must be written in terms of metal concentration over a given length. For example, 15 g/t of gold over 2 meters. While these are only two dimensional snapshots of a gold mineralized area, enough of them in one vicinity are combined to form a three dimensional graph of the tonnage and grade of the gold deposit.
Longitudinal Section