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By Natalie Caciagli

Catchment basin sampling allows for rapid assessment of large areas. Stream sediment surveys are a common tool used in regional exploration. The difficulty in detecting geochemical anomalies in stream sediment data from large regional datasets lies in finding the background values of pathfinder elements due to variable lithologies that could be sampled within a single basin. An alternative data driven method to discover anomalies in complex environments, without a priori knowledge of background concentrations, is presented here

May 10, 2023

By Andrei Bagrianski, Marco Nieto, Alexander Prikhodko

Se realizó una adquisición magnetotelúrica helicotransportada con el sistema MobileMT sobre un depósito metálico asociado a un pórfido de cobre conocido como Proyecto Santiago en el Cinturón Metalogénico Mioceno al sur de Ecuador. La adquisición geofísica se enfocó en identificar las respuestas de magnetometría y conductividad eléctrica y paso seguido, realizar inversiones unidimensionales y bidimensionales con el objetivo de caracterizar la respuesta petrofísica del sistema tipo pórfido. Los resultados arrojaron una anomalía de conductividad aparente mayor a 15 mS/m que se identificó como el cuerpo porfirítico en profundidad, llegando a estar entre 200 m a 600 m por debajo de la superficie.

May 10, 2023

By Robert Gordon, Leduar Ramayo

This paper reviews the application of the magnetotellurics method for deep earth imaging, specifically its recent use to better understand original mineral emplacement processes. Resistivity information from newer innovative applications of the technology for nearer surface imaging also provides valuable insights into near surface structure, which in some cases has led directly to new discoveries.

May 10, 2023

By Rafael Ramos, Leonel Quispe, César Chávez

El programa de trabajo de campo realizado consistió principalmente en el cartografiado de la concesión minera EMADSUR I y el muestreo de estructuras (vetas y cuerpos). Los resultados preliminares del estudio geológico en el proyecto Livitaca confirmaron la presencia de mineralización tipo skarn y tipo pórfido de Cu-Mo-Au con diseminación de sulfuros rodeado de un amplio halo de alteración fílica-argílica. Vetas angostas, principalmente entorno de los cuerpos de skarn, tienen contenidos elevados de Au-Cu-Pb-Ag.

May 10, 2023

By Aldo Bendezú

En el Perú, el cobalto @>0.1% de concentración se da principalmente en sistemas hidrotermales, particularmente en yacimientos de tipo IOCG y en vetas altoandinas de Zn-Pb-(Ag)-Ni. El primer tipo se presenta en al menos dos segmentos del cinturón de yacimientos IOCG de la costa, entre Lima e Ica. El segundo ha sido documentado principalmente en la Cordillera Oriental, entre Huánuco y Puno. Se han identificado 29 sistemas de vetas y mantos significativos entre ambos tipos. En las vetas, estos ocupan porciones restringidas de 100-500 m de largo, 50-200 m de alto y 0.2-1.5 m de potencia, sugiriendo masas prospectivas del orden de 0.2-0.5 Mt por cada sistema.

May 10, 2023

By Patrice Baby, Joselyn Medina

Recent reports indicate potential for metallic mineralization in the Ucayali Subandean fold and thrust belt related to a mineral system with a magmatic source. In this work, we show the control of Andean tectonics in metallic mineralization in Ucayali and discuss the key components of the mineral system.

May 10, 2023

By Patrice Baby, Stefano Salvi, al et, Jean Vallence, Galdos, Renzo

The nature of the gold-bearing fluid and the source of gold in sedimentary-hosted gold deposits of Carlin, orogenic or epithermal types is still matter of debate. Most authors point to magmatic/ metamorphic origin for the fluids, however, the properties of such fluids and their interactions with organic carbon – a common component in this type of deposits – are not sufficiently well known. Here we present a large set of novel geochemical, mineralogical and fluid-inclusion data obtained from the Algamarca Au-Ag-Cu epithermal veins, corresponding to lateral manifestation of the neighbouring sedimentary-hosted epithermal-gold deposit at Shahuindo.

May 10, 2023

By Jorge James

En los últimos 20 años la conflictividad social alrededor de las minas y proyectos mineros ha aumentado debido a diferentes razones. Haciendo un análisis de los conflictos se pueden extraer lecciones que sirvan a las empresas mineras para evitar, o al menos mitigar, conflictos futuros. Esta lista de 50 lecciones puede servir como una guía de lo que hay que hacer, de lo que hay que evitar, o por lo menos de qué temas se deben tomar en cuenta al momento de desarrollar un proyecto minero.

May 10, 2023

By Jorge Spangenberg, Lisard Torró, Patrick Quispe, al et, Johan Ramírez

Presentamos nuevos datos de isótopos estables de carbono y oxígeno que ayudan a delimitar el origen y la evolución de los fluidos del estadio C en el depósito de Zn-Pb-Ag-In-Sn-Cu de tipo cordillerano de Ayawilca. Los datos isotópicos de rodocrosita hidrotermal indican que los fluidos mineralizantes presentaron valores promedio de 13C y 18O de -13 ‰ (VPDB) y 19 ‰ (VSMOW), respectivamente.

May 10, 2023

By Haizea Arratibel, Diana Méndez, Jhuliana Macas, Michelle Peñaherrera

La forma en la que las empresas ingresan a un territorio sienta las bases para las dinámicas de relacionamiento a futuro. El diálogo multiactor es una herramienta que permite, desde un inicio, formar relaciones de confianza y acción colectiva, pasando así de una dinámica transaccional a una transformacional. Esto alcanza resultados que van mucho más allá de la gestión de conflictos, enfocados a crear un territorio sostenible bajo un modelo de gobernanza sólido. Se presenta el caso del proceso de diálogo multiactor en Los Encuentros, Ecuador, bajo el marco del proyecto Fruta del Norte de Lundin Gold.

May 10, 2023

By Miguel Tapia, Javier Alfaro, al et, Boris Alarcón, Sergio Giglio

El Proyecto Cachorro está ubicado a 150 Km al NE de la Ciudad de Antofagasta, en la Cordillera de la Costa de la Segunda Región de Chile, donde se encuentran depósitos de cobre tipo estratoligados, IOCG, y pórfidos (Mantos Blancos, 500 Mton @ 1,0% Cu; Antucoya, 1.200 Mton @ 0,3% Cu) (Fig. 1). El descubrimiento es el resultado de campañas de exploración greenfield en áreas cubiertas efectuadas desde 2013 por AMSA en el norte de Chile. El depósito se aloja en rocas estratificadas sedimentarias y volcánicas del Paleozoico superior al Jurásico inferior e intrusivos y brechas hidrotermales del Jurásico inferior que se relacionan temporalmente con la mineralización.

May 10, 2023

By Miguel Tapia, al et, Milenko Gonzalez, Sergio Giglio

El Encierro es un yacimiento de tipo pórfido Cu-Au del Mioceno superior ubicado en la zona intermedia entre las franjas de El Indio y Maricunga, en el norte de Chile. Está emplazado bajo un extenso lithocap que presenta evidencias de mineralización de tipo epitermal de alta sulfuración y que fue explorado entre 1987 y 2010 por varias empresas. En 2016, AMSA firmó un contrato de opción de compra con Barrick con el objeto de comprobar la existencia de un sistema tipo porfídico en profundidad con potencial económico. Cuatro campañas de perforación desarrolladas entre 2015 y 2020 permitieron probar que debajo del lithocap se encuentra un sistema porfídico de Cu-Au con leyes que se incrementan por debajo de la cota 3,000 m.

May 10, 2023

By Jorge Barreda, Gutiérrez, Elliot Hidalgo, Anthony Pérez, José

En la industria minera es usual incrementar Recursos Minerales en función de planes de perforación diamantina. Estos programas generalmente se orientan a los sectores de Recursos Inferidos o Mineral Potencial con leyes y/o NSR mayor al cutoff de Recursos Minerales. La metodología desarrollada en el presente trabajo permite incorporar el análisis técnico-económico y la incertidumbre geológica en la evaluación de la viabilidad de los programas de perforación con el mayor Valor Presente Neto (VPN) y con el menor Riesgo Geológico (a través del uso del Valor en Riesgo – VaR).

May 10, 2023

By Joaquín Copaja

Highly fertile magmatic conditions for porphyry copper formation, such as high water content, can be recognized in zircon trace element chemistry using proxies as the 104(Eu/Eu*)/Yb ratio. Due to their resistance to alteration and long-distance transport, zircons hosted in sedimentary sequences can be used to assess fertility over large detrital source areas. Herein we present a study based on LA-ICP-MS analyses of zircons derived from post-Oligocene sedimentary sequences cropping out across the Paleocene-Eocene Cerro Colorado district of Northern Chile. U-Pb dating on individual detrital zircons yielded ages ranging from Jurassic to Miocene, concordant with the district geology. Subsequent fertility assessment recognized several peaks in the magmatic hydration over time.

May 10, 2023

By D. F. Malan, J. A. L. Napier

A number of shallow coal or hard rock mines employ pillar mining systems as a strategy for roof failure control. In certain platinum mine layouts, pillars are designed to ‘crush’ in a stable manner as they become loaded in the panel back area. The correct sizing of pillars demands some knowledge of the pillar strength and the overall layout stress distribution. It is particularly important to understand the impact of the layout geometry on the effective regional ‘stiffness’ of the rock mass around each pillar. An important design strategy is to model relatively detailed layout configurations which include a precise representation of the local pillar layout geometry and to analyse multiple mining scenarios and extraction sequences to select optimal pillar sizes and barrier pillar spacing. Although computational solution techniques are now impressive in terms of run time efficiency, a major difficulty is often encountered in assigning suitable material properties to the pillars and in devising an effective material description of the layered rock strata overlying the mine excavations. This paper outlines an efficient numerical strategy that can be used to assess large-scale pillar layout performance while retaining the ability to modify individual pillar constitutive behaviour. The proposed method is applied to selected layouts to compare estimated average pillar stress values against values determined by detailed modelling and against observed behaviour.

May 3, 2023

By D. F. Malan, D. Ile

This study explores the use of backfill in hard rock bord-and-pillar mines to increase the pillar strength and extraction ratio at depth. The use of backfill will also minimize the requirement for tailings storage on surface and the risk of environmental damage. A literature survey indicated that backfill is extensively used in coal mines, but rarely in hard rock bord-and-pillar mines. To simulate the effect of backfill confinement on pillar strength, an extension of the limit equilibrium model is proposed. Numerical modelling of an actual platinum mine layout is used to illustrate the beneficial effect of backfill on pillar stability at greater depths. The magnitude of confinement exerted by the backfill on the pillar sidewalls is unknown, however, and this needs to be quantified using experimental backfill mining sections equipped with suitable instrumentation.

May 3, 2023

By D. F. Malan, P. M. Couto

We propose a layout design for the UG2 Reef where weak geological alteration layers are present. The collapse of the Everest platinum mine in South Africa indicated that these layers substantially weaken the pillars. The popular Hedley and Grant pillar strength formula cannot be used where these alteration layers are present. Underground investigations at Everest mine and numerical modelling of the layout were conducted using the TEXAN code and a limit equilibrium model. Simulations of a collapsed area and an intact area allowed for a preliminary calibration of the model. This was subsequently used to explore modified layouts for these ground conditions. An alternative is to compartmentalize the blocks of ore using barrier pillars. The numerical modelling predicted that the barrier pillars appear to remain stable even in the case of large-scale collapses, provided their width exceeds 25 m. Main access routes into the mine can be protected by a double row of pillars at least 15 m wide to provide a safe travelling way. As a cautionary note, these conclusions are based on the model calibration and this needs to be refined in future. Calibration of the limit equilibrium model remains a challenge owing to the large number of parameters involved.

May 3, 2023

By J. A. Maritz, D. F. Malan

Pillar strength is affected by pillar shape, but this has largely been ignored in past research studies. Bord-and-pillar layouts are typically designed using empirical strength equations developed for square pillars. Owing to the poor quality of pillar cutting, many hard-rock pillars have an irregular shape and it is not clear how this affects pillar strength. Furthermore, the strength of rectangular pillars in comparison with square pillars is also difficult to quantify. The ‘perimeter rule’ is widely adopted for rectangular pillars, but its applicability for pillars with irregular shapes has never been tested. We used numerical modelling in this study to investigate the effect of pillar shape on strength. An analytical limit equilibrium model of a square and a strip pillar also provided useful insights. For slender pillars, the strength of a long rib pillar is essentially similar to that of a square pillar. In contrast, for rib pillars with a large width to height ratio, there is a substantial increase in strength. The study found that the perimeter rule should not be used for irregularly shaped pillars. Displacement discontinuity modelling, using a limit equilibrium approach, is proposed as an alternative to determine the strength of these pillars.

May 3, 2023

By F. J. N. Bruwer, T. R. Stacey

The research described considers whether the variability in coal material strength, as derived through a series of uniaxial compressive strength (UCS) tests, could be used to indicate the variability in coal pillar strength. The aim is to be able to use a distribution of UCS tests as input into the coal pillar strength calculation. This will allow the pillar design to be expressed in terms of a probability of failure rather than as the commonly used safety factor. To achieve this, the bulk strength factor associated with commonly used pillar strength formulae was replaced with a distribution of UCS results divided by an adjustment factor. The factor was determined so as to ensure that the resulting bulk strength does not deviate from the statistically determined bulk strength published in the original formulae. This approach enabled pillar strength distributions to be obtained using industry-accepted strength formulae, subsequently allowing for a probability of failure to be calculated for a specific pillar design. Using a regional coal material strength curve as a baseline, coalfields in which the coal is stronger than the regional mean can be identified and the pillar designs optimized. This is based on the stronger coals achieving lower probabilities of failure at similar safety factors. The research has considered actual UCS data from multiple mines in the Mpumalanga coalfields of South Africa, and has proved that the variability in material strength between coalfields could allow for some optimization using the proposed approach. Based on the data used in the study, a 2.78% increase in extraction could be achieved. However, further research will be required to validate the results of the study in an underground environment.

May 3, 2023

By D. F. Malan, R. P. Els

The limit equilibrium model, used in displacement discontinuity codes, is a popular method to simulate pillar failure. This paper investigates the use of physical modelling to calibrate this model. For the experiments, an artificial pillar material was prepared and cubes were poured using the standard 100 mm × 100 mm civil engineering concrete moulds. The friction angle between the cubes and the platens of the testing machine was varied by using soap and sandpaper. Different modes of failure were observed depending on the friction angle. Of interest is that significant loadshedding was recorded for some specimens which visually remained mostly intact. This highlights the difficulty of classifying pillars as failed or intact in underground stopes where spalling is observed. The laboratory models enabled a more precise calibration of the limit equilibrium model compared to previous attempts. Guidelines to assist with calibration of the model are given in the paper. The limit equilibrium model appears to be a useful approximation of the pillar failure as it could simulate the stress-strain behaviour of the laboratory models.

May 3, 2023