Estudo para implantação de perfilagem geofísica aos poços de sondagem da mina de fosfato de Tapira-MG

Abstract

Geophysical logging obtains the physical properties of rocks, continuously outlining the differences along the geological profile. When integrated with a Mineral Research program, it can support strategic decisions, reducing the risk of a mining project. In mining planning, it contributes to assertive plans and higher quality in reconciliation. During the evaluation of resources and reserves, it is important to determine the ore density systematically. In conventional tests, samples with low resistance can break during handling in the laboratory. Obtaining the density in situ with the application of geophysical logging in core drilling is advantageous when the recovery of cores is poor or non-existent, in the case of a friable to semi-compact ore. This study followed a pilot implementation of geophysical logging techniques in drilling wells at the Tapira-MG mine (Mosaic Fertilizantes), which has phosphate ore originated from supergene enrichment in saprolite zones. The theoretical applicability of geophysical logging was studied, analyzing the efficiency of the process and the responses to the data from the rock core. The methodology consisted of field monitoring of gamma-gamma and natural gamma density tools; in scenarios with and without drilling metal support and with and without a radioactive source. The contacts identified in the description of the cores were compared, regarding compositional and textural changes in the cores, with the responses in the geophysical profiles, seeking to evaluate the horizons of weathering alteration, the mineralized interval and the signatures. The preliminary results showed that the geophysical methods may not be efficient in detecting mineralized zones (a marking in the intervals of phosphate enrichment is still unclear), but it identifies general contrasts between the mineralogical properties and the changes in the weathering horizons. The tool does not replace the data from drilling (geochemistry and geological description), but it can be auxiliary and complementary. Although more detailed and quantitative analyses are still necessary, so far the comparative results suggest that logging helps in determining depths, guiding the positioning of geological contacts and sampling intervals. Regarding density measurement, the method can be applied especially when there are no intact samples for laboratory testing, or when there is low recovery of cores, but geostatistical and calibration studies are still ongoing. As this is an initial step for logging to become operational, disadvantages already mapped by the study more time to obtain data in the field, in addition to safety controls, since handling a radioactive source requires trained staff, adequate storage infrastructure and presents a risk of entrapment in the well, which makes the use of the natural gamma method more strategic.