Steinar Ellefmo

The Value of Information in Mineral Exploration Within a Multi-Gaussian Framework

In mineral resource evaluation a careful analysis and assessment of the geology, assay data and structural data is required. One important question is where to position the exploration boreholes, another is what method to use when analyzing the grade in the collected material. Here, a challenge of this type is whether one should analyze the collected core samples with accurate and expensive lab equipment or a simpler hand-held meter. A dataset of about 2000 oxide observations is available, along with relevant explanatory variables, from a deposit in Norway. A Gaussian geostatistical model is used to predict the grade parameter on block support. To improve the predictions, several new boreholes are planned, giving 265 additional samples. The associated uncertainty reduction is evaluated, and a resource evaluation is performed with and without the planned data. Then the value of information of the planned data is computed, using assumed costs, recovery rates and revenues. The data acquired with the hand-held meter has almost the same value as the more expensive acquisition strategy, given that the already established correlation between the two datasets is valid.

ROV based drilling for deep sea mining exploration

Exploring for minerals on the seabed is challenging — and the ability to collect representative sub surface samples is essential. The research project MarMine led by NTNU has together with Seattle based Williamson and Associates developed and tested an ROV-based drill rig for mineral (seafloor massive sulfides) and rock sampling. The ROCS system is a single stroke drill and is simple, robust and possible to use from various larger ROVs. For the vehicle to provide a stable platform, the vertical bollard pull of the ROV and the vehicle mass are important variables. The developed drill uses a thin wall drill bit and barrel and operates at high RPM to reduce the required down weight and drilling moments. The system also contains an emergency release to be used if the core barrel is stuck. The drill is hydraulically powered with cylinders operating the tower and a rotation unit. It can rapidly be modified to provide samples from softer samples like unconsolidated material. At the Arctic Mid Ocean Ridge, a work class ROV was deployed with the drill mounted for testing at 2700 m depth in basalt rock. The recovery from the system was above 80%. Such core samples can be used for chemical analyses of metal and mineral grades, mineralogy and rock mechanical testing. The system provides a probing tool for marine mineral exploration, with low cost, low operational complexity and low risk. Proper resource estimation requires drilling deep into the deposit, but the one meter deep core samples provided by the ROCS will provide valuable a priori information planning for more extensive drilling campaigns.