USING VULCAN 3-D SOFTWARE FOR BULK MINEABLE GRADE CONTROL (CARLIN-TYPE GOLD)

Located on the Battle Mountain-Eureka Trend, the Cortez Hills Mine (operated by Barrick Gold) is a uniquely mineralized Carlin-Type Deposit. Carlin-Type Deposits are sediment hosted, disseminated gold deposits associated with arsenic and thallium. Typically, these structurally complex deposits are located along range-front faults and are silicified; alteration at Cortez is decalcification. Cortez has several related, but geometrically distinct ore bodies being mined via both open pit and underground operations. Within the open pit operation (CHOP), there are two deposits in one pit; continuous mining occurs across the deposit boundaries. Each deposit has its own structural orientation (attitude) thus requires specific estimation parameters for ore routing.

CHOP uses Vulcan 3-D modeling software for daily grade control processes. Blast hole samples are imported from a database into Vulcan by blast pattern name. Each pattern has a unique ID and contains around 75 off-set drill holes. Once imported, blast holes are compared to a preset grade control classification using a grade control variable file (GCV). The GCV color-codes the loaded blasts into designated bins based on grade, preg robbing potential, and aa/fa ratio. The blast holes are then estimated into a block model.

CHOP contains two deposits within one pit. We have classified these as Region 1 and Region 2, defined by an arbitrary boundary. (The boundary was placed in an area of no known mineralization where structural orientations began to vary.) Samples falling within a Region are flagged through a block estimation file then estimated along the predefined attitude for that Region. By changing the sample selection variography, a geologically accurate model is generated. These models allow for more precise ore cuts (used for routing material into grade bins). Until recently, the search orientation used for the entire pit was a 50’ sphere, potentially diluting material.  By forcing the search orientation along the average attitude of each Region, we see less dilution and greater gold recovery. This method is new to CHOP and has only been used in Region 2. Further testing is required to verify if these conditions will be favorable for Region 1 as well.