Abstract Artisanal and Small-scale Mining (ASM) is a prominent activity in the extractive industry: considering only gold, it produces about 20% of the world market supply. Despite this fact, ASM is generally associated with the negative aspects of its environ mental impact, and operational research is generally neglected. This article empha sizes the peculiarity of the drilling and blasting systems of small underground mines in selected South American Countries. Such Countries, while having large mineral deposits and well recognized large-scale mining activities, at the same time still pres ent on their territory ASM activities that are archaic, highly inefficient and dangerous for the safety of its operators. This article documents drilling and blasting activities from gold mining in Ecuador and Chile. First, described are the outdated and often non-rational techniques employed by miners, to provide a general framework of the current methods. Then, shown is what can be improved and how the current methods can be modified. Finally, some field applications and the comparisons of the results ob tained are presented. One case shows how blast pull efficiency can be increased from 82% to 98% by changing non-rational applications of explosive products to rational, scientific-based employment. Another case shows how, by rationalizing blast designs, drilling and blasting costs can be reduced by 9% per month, the advance by blasting increased by 29% and the pull efficiency increased from 70% to 90%. Finally, it is concluded that examples of application show how operational improvements are eas ily applicable in the field, relying only on tools and resources of artisanal mining, but combining solid engineering bases with confidence-gain and respect for the experience of the miners.

Abstract One of the most characteristic aspects of artisanal mining is the lack of geological exploration. Going into production without previous exploration is here defined as a gambling scenario. The present study intended to quantify the risk associated to such gambling by analyzing the operations of an area of artisanal underground gold mining in central Chile. To quantify the risks and the probable outcomes, a risk analysis technique called Event Tree Analysis has been applied. This technique is based on the analysis of possible multiple outcomes of single events or decisions and the probability of occurrence of each. Results show that chances of negative vs. positive revenue are 83% vs. 17%, with an order of magnitude of difference between worst-case and best-case scenarios.

Abstract This article deals with a study performed at the Experimental Mine of the Research Center of Responsible Mining of the University of São Paulo, to examine the correlations between geological environment, blasting parameters and energy consumption in the primary crushing phase. The research is designed to appreciate the relationships between the energy provided for size reduction and the resistances to size reduction. For this purpose, Key Performance Indicators (KPIs) are used to describe the possible improvements on the energy consumption due to crushing. Four blast tests were performed: for each blast, KPIs were recorded regarding the blast design, the particle size distribution, the real power energy consumption at the primary crushing unit and its rate of utilization. The results show that energy consumption at the primary crusher is a sum of two components: energy directly involved in crushing the rock, and additional energy used for winning the inertial resistances of the moving parts of the crusher. We show how explosive energy and delay times influence the production of coarse fragments that jam the crusher, therefore influencing machinery stops and inertia loads related to putting the jaws back into movement.

Abstract Rock blasting is the first phase of comminution, completed by mechanical means downstream in the crushing and milling phases. Nevertheless, mineral processers and blasters seldom work together. The total energy of mechanical comminution depends on feeding grain size and on the internal resistance of the material to grinding. Blasting heavily influences both of these aspects: i) it induces visible fracturing: this is the particle size distribution visible to the naked eye, that is measurable by means of image analysis or sieving; ii) it induces invisible fracturing: this is the system of micro-fractures, invisible to the naked eye, that are detectable only by microscopic analysis but show their direct effect by reducing the grinding energy ("softens" the material). A proper management of blasting can greatly benefit the comminution circuit. In this article, the author analyzes data from literature and from field experiments and discusses the benefits that rock blasting can produce for the comminution process.

Abstract This paper shows the work conducted at the Experimental Mine of the Research Center of Responsible Mining of the University of São Paulo, taking into account the theoretical issues presented in the first part of the article. The research was performed without changing the production cycle and without resorting to investments in new types of equipment: it has attempted to increase the productivity of the quarry, by lowering production costs and improving the quality of the product. Some Key Performance Indicators (KPIs) were established to monitor the results. A new blast design method, a more appropriate initiation sequence and some simple, inexpensive and effective solutions were identified and applied. The results show that the proper selection of delay timing can be of significant benefit to downstream processes as well as enhanced fragmentation itself.

Drilling and blasting are fundamental operations in the mining cycle and consti tute an important component of the mining costs. Rock fragmentation can in principle be managed by means of two options: by increasing or reducing the specific consumption of explosives, or by modifying the drilling pattern. The choice of one or other type of control depends on the relationship between the unit costs of drilling and explosives, and on technical restrictions or regulations imposed by different reasons. It is then necessary to identify the link between the blast design and some factors affecting the downstream processing of the product. This paper analyzes the theoretical basis aimed at evaluating the main parameters involved when organizing a production blast in open pit quarries. In particular, a method developed through the analysis of the results in a large number of limestone open pit quarries in Italy is described and commented. The first experimental results in Brazil have been obtained by applying this method at the Experimental Mine of the Research Center of Responsible Mining of the University of São Paulo. Experimental methods and results will be analyzed and discussed in the second part of this paper.

Atualmente no mundo, devido ao elevado preço do ouro, milhares de pequenas minas artesanais operam sem a capacidade financeira ou técnica para atualizar seus métodos de produção, muitas vezes utilizando equipamentos e métodos de lavra que foram abandonados há décadas na indústria mineral convencional. Esse artigo ilustra, com um exemplo prático, que é possível atingir os modernos requisitos de qualidade, segurança e produtividade, mesmo operando com equipamentos de lavra que possuem basicamente as mesmas características dos utilizados na década de 1950. A operação envolveu a escavação de um túnel de 6 metros e o desmonte de mais de 25 seções em rocha e concreto, em uma mina de ouro subterrânea. O artigo descreve como os principais problemas operacionais foram superados: a concepção de um padrão de perfuração eficaz que foi facilmente alcançável com o limitado equipamento local, a previsão do comportamento e a gestão do local explosivo com base em nitrato e a interação com as equipes de perfuração, a fim de determinar um ponto de acordo entre seus métodos de trabalho tradicionais e a visão científica do engenheiro. No final do artigo, são propostas algumas diretrizes gerais para a gestão de situações semelhantes, a fim de serem melhoradas a eficiência, a produtividade e a segurança das operações de perfuração e desmonte em minas subterrâneas de pequena escala.

In the world today, due to the current high price of gold, thousands of artisanal small-scale mines operate without the financial or technical capacity to upgrade their production methods, often using equipment and working methods that were forsaken decades ago in the conventional mining industry. This article illustrates, with a practical example, that it is possible to achieve the modern requirements of quality, safety and productivity, while operating with mining equipment that basically possesses the same characteristics as that employed in the 1950s. The operation involved the excavation of a 6 meter long tunnel and over 25 stoping sections in both rock and concrete by drilling and blasting in an underground gold mine. The article describes how the main operational problems were overcome. An effective drilling pattern was designed in order to be easily achievable with the limited local equipment. The behavior of the local nitrate explosive was effectively predicted and managed. The interaction with the drilling teams was managed in order to determine a meeting point between their traditional working methods and the scientific view of the engineer. At the end of the article some general guidelines are proposed for the management of similar situations, in order to improve the efficiency, productivity and safety of drill and blast operations in small-scale mines.

Esse trabalho descreve a pesquisa sobre a aplicação de análise de complexidade para avaliar o desempenho do processo de desmonte de rocha na mineração. O objetivo principal da pesquisa é o desenvolvimento de um método que permita identificar uma solução robusta para gerenciar a fragmentação do desmonte e para planejar o processo de forma a alcançar as metas de produtividade da britagem. A pesquisa utiliza ferramentas de análise de complexidade, introduzindo uma abordagem particular de sistemas complexos inédita em mineração e em aplicações de desmonte. Os resultados alcançados indicam que a compreensão adequada das correlações entre as variáveis-chaves no desmonte traz benefícios importantes para apoiar a tomada de decisão no ambiente de alta incerteza do processo de desmonte de rocha. A busca por um sistema robusto se mostrou mais relevante do que a busca por uma solução teoricamente ótima, já que os níveis de robustez e de complexidade podem ser utilizados para comparar diferentes modelos e para medir a aderência desses modelos aos dados de campo.

The paper describes the research carried out in the application of complexity analysis in order to evaluate the performance of the rock blasting process in mining. The main objective of the research is the development of a new method to allow the identification of a robust solution for managing rock fragmentation and to plan the process so that productivity targets can be achieved. The research uses complexity analysis tools introducing a particular approach for complex system analysis in mining and in rock blasting. The results indicate that the proper understanding of the correlations between the key-variables in blasting provides important benefits in the decision making process in the highly uncertain environment of rock blasting. The search for a robust system has proven to be more relevant than the search for a theoretically optimum solution, as the levels of robustness and complexity can be used to compare different models and to measure the adherence of such models to the actual field data.