Correlations in geological model and Titan 24 DCIP_MT at the Bolivar skarn

mineralization, Mexico

Leduar Ramayo 1, Roger Sharpe 1, Mehran Gharibi 1, Alonso Lujan2

1 Quantec Geoscience LTD. 146 Sparks Avenue Toronto, Ontario M2H 2S4, Canada 2 Sierra Metals, Chihuahua, Fernando de Borja No. 100. Col. San Felipe, Chihuahua, Chihuahua, México

Resumen

Bolívar es un depósito polimetálico, el cual se explota subterráneamente y se localiza en Chihuahua, México. La exploración Brownfield ha jugado un papel muy importante en el desarrollo de los recursos minerales en la mina Bolívar. En los años 2011 y 2017 se llevaron a cabo estudios geofísicos con la tecnología Titán 24 para ayudar a mapear la extensión de la mineralización de skarn asociada a mantos de reemplazamiento. Los estudios detectaron más de 40 áreas de interés que requieren mayor investigación y perforación. El modelo de inversión 3D de los datos proporcionó una excelente herramienta para la exploración y resalta la estructura general del depósito, además detectó varias zonas prospectivas al norte del depósito. Este trabajo muestra algunas correlaciones entre el modelo geológico del proyecto y los resultados de los métodos de exploración aplicados, los cuales están dando como resultado una exploración exitosa del proyecto Bolívar.

Abstract

Sierra Metals’ Bolívar Mine is a polymetallic deposit that is mined underground located in Chihuahua, Mexico. Brownfield exploration has played a very important role to drive a potential expansion of mineral resources. High-value drill targets are identified using a combination of geophysical, geological and geochemical exploration methods. A Titan 24 geophysical survey was carried out to assist in mapping the extent of mantos replacement and structures containing copper and copper / zinc skarn mineralization for drill targeting in the immediate vicinity of the Bolivar mine. The survey highlighted over 40 specific areas of interest requiring further investigation and follow up. The 3D inversion modelling of the data provided an excellent tool for further exploration and highlights the overall structure below the deposit, in addition to similar structures and mineralization to the north of the deposit. This paper will demonstrate some correlations between survey methods that are resulting in successful targeting.

1. Introduction

Sierra Metals’ Bolívar Mine is a copper-silver-zinc-gold deposit that is mined underground using the room-and-pillar mining method. Skarn alteration and mineralization at the Bolivar property is hosted primarily in Late Cretaceous – Early Cenozoic sedimentary and volcanic rocks that underlie the Piedras Verdes Mining within the Sierra Madre Precious Metals Belt that extends across Chihuahua, Durango and Sonora in northwestern Mexico. The Bolivar deposit is one of many precious and base metal occurrences in the Sierra Madre precious metals belt, which trends north-northwest across the states of Chihuahua, Durango, and Sonora.

1.1. The Titan 24 Survey

Quantec’s 24-bit TITAN-24 distributed acquisition system is deployed with 100 m E-field dipoles along each line. An orthogonally oriented E-field measurement is collected at every other dipole. The line setups consist of nominally twenty four (24) E-field dipoles oriented along the survey line and twelve (12) dipoles perpendicular to the line. To collect the MT data, one set of H-field measurements is recorded for each setup. All data are recorded as time-series information. The time-series data are downloaded to a processing computer and archived to DVD. The time-series data are processed daily to raw data plots of DC, IP and MT geophysical parameters using proprietary Quantec time-series processing software. The Titan 24 DCIP data collection and signal processing use a sophisticated digital signal processing methodology (Sharpe et al, 2017). The data are collected using a 100 % duty cycle with a transmitter pulse length of 256/30 seconds (approximately .1 Hz) in a 60 Hz powerline environment. The DCIP data are digitized at 240 sps and the acquisition is monitored and processed in real-time, in order to maintain quality control.

The Bolivar survey grid (Figure 1) consisted of a total of 12 lines which were 26.5 km in length. Each line had a 100 m dipole spacing and was located 200 m from the line adjacent.

Figure 1.

2. Survey Results

Results from southern line survey are shown in Figure 2. Note the deeper depth of investigation due to the longer survey lines. Bolivar West has a strong shallow signature and the Bolivar Mine has a deep, flat-lying signature. Figure 2 shows an IP result survey for the northern extension of the Bolivar Northwest mineralization. Note the depth and steepening dip of the mineralization and the abrupt termination on a steep fault.

Figure 3 shows the MT resistivity results from the same survey line shown in Figure 2. The deep resistivity response clearly maps both the aspect and location of the mineral offsetting fault. Structural characteristics under the deep part of Bolivar West are very different from the basement under the Bolivar Northwest extension.

Figure 2. Deep IP results showing the Bolivar

Northwest extension.

3. Conclusions

Despite that geology is sub-horizontal and initially known target horizons and mineralization style were relatively shallow, extended depth of investigation was of value on this property. Drivers, heat sources and feeder faults were all better mapped both by the extended length DCIP survey lines and by the deep penetrating MT. The surface culture environment is dense, active and distorts the data. Annotated sections and plans showing all the cultural features eliminated miss-interpretation and permitted deep mapping near mine. Don’t discount those ‘isolated anomalies’ in the center of the section (sections 1400 and 1600). Stand-alone, isolated anomalies are

always suspected as artefacts in geophysical interpretation. Titan-24 can provide a deep penetrating alternative and corroborating resistivity measurement in the MT.

Figure 3. MT resistivity results from the same survey

line shown in Figure 1.

References

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NOTASCORRELATIONS IN GEOLOGICAL MODEL

AND TITAN 24 DCIP_MT AT THE BOLIVAR SKARN

MINERALIZATION, MEXICO

Leduar Ramayo , Roger Sharpe ,

Mehran Gharibi , Alonso Lujan