Integrating multiple lines of evidence to define the exploration target range for the Castelo de Sonhos Paleo-placer gold Project, Brazil

Integrating multiple lines of evidence to define the exploration target range for the Castelo de Sonhos Paleo-placer gold Project in Brazil

Castelo de Sonhos, a gold deposit in Pará State, Brazil, has seen several phases of exploration since the mid-1990s. These programs have provided drill hole data, surface mapping of outcrops, geophysical surveys, geochemical surveys of soil samples and preliminary metallurgical test work. But 20 years after the deposit was first drilled, its resource potential was still not well quantified. The first 43-101 resource estimate created the impression that the project had only a modest resource potential … unfortunate for a deposit where the drilling has not yet encountered the edge of mineralization in any direction, and where only 25% of the strike length of the mineralized unit, a conglomeratic band, has been drilled.

This year, a new approach has been taken to quantifying the project’s risk and its potential. All available data from the exploration programs have been integrated with recent advances in paleo plate reconstructions, in modeling fluvio-deltaic systems, in geostatistical simulation, and in data mining. This integration of ideas and methods from the petroleum industry, from geostatistics, from classical statistics and from plate tectonics makes it possible to quantify the exploration target in the manner required by National Instrument 43-101: as a range of possible tonnages and grades. Although preliminary resource estimates for the project had already been reported, defining the exploration target has the benefit of establishing an appropriate understanding of the scale of the project. Not only does this improve scoping studies and preliminary economic assessments, but it also assists in financing a project once regarded as being too small by many mining companies. 

The talk will discuss the benefits of quantifying the exploration target range. It will present the exploration concept for Castelo de Sonhos, showing how it is well-grounded in data, in field observations and science. After explaining the multiple lines of evidence that contribute to the exploration target, the talk will discuss how this conceptual model is testable through drilling and surface trench sampling, concluding with a discussion of the next phases of exploration.

R. Mohan (“Mo”) Srivastava is a geologist who knows enough about numbers to be called a geostatistician. He once planned on being a sedimentary geologist in the petroleum industry, but ended up becoming a resource estimation specialist after he broke his leg in a motorcycle accident. For the past 30+ years, he has been regarded as high-risk borrower by banks, who take the view that if you’re self employed then you’re unemployed. He remedied this problem late in 2015 by becoming Vice President for TriStar Gold, the junior mining company that is developing the Castelo de Sonhos project.

Mo has a B.Sc. in Earth Sciences from MIT, and an M.Sc. in Geostatistics from Stanford University. He is a co-author of the widely-used textbook An Introduction to Applied Geostatistics. In the 32 years since he last had a real job, Mo has provided consulting services to a wide range of mining projects throughout the world. In his consulting work with the petroleum industry, he developed the fluvio-deltaic modeling tools that have now found use in establishing the exploration target range for a hard rock gold project.