Jacopo Seccatore

An estimation of the artisanal small-scale production of gold in the world.

The increase in gold price of over 400% between 2002 and 2012, due to a shift towards safe investments in a period of crisis in the global economy, created a rapid increase in gold production. A response to this shift in production was observed for artisanal and small-scale mining (ASM) units in remote locations of the world, but this phenomenon has not been quantified yet. The work presented here was done to provide a quantitative tool for estimation of the gold (Au) produced by ASM and the population of workers involved in the production process, and assessment of mercury (Hg) consumed. The following hypotheses were addressed: i) It is possible to estimate, on first approximation, the amount of Au production in the world by artisanal mining; ii) Au production by artisanal mining varies by country and continent and iii) Hg consumption due to ASM can be correlated with the methods applied in the different countries and continents for the production of Au. To do this we estimated the number of miners, calculated the change in Au price and production and then applied an adjustment factor to calculate Hg production by country and continent. The amount of Au produced depends on technology of the miners by continents (highest in South America, medium in Asia and Central America, and lowest in Africa), and the geologic setting (not investigated here). The results of the estimation show that, as of 2011, over 16 million Artisanal Miners, in the world, were involved in gold extraction (mining or treatment), producing between 380 and 450 t of gold per year, with clear global behavior between the continents in terms of recovery efficiency, confirmed by data on Hg release that is higher in countries with lower technology.

Efficiency as a Road to Sustainability in Small Scale Mining

The world is going through a new-millennium rush in precious metals, especially gold. The great increase in gold price in the last years, probably due to a shift towards safe investments in a period of crisis in the global economy, created a rapid increase in gold production. The faster response to this shift in production came from Artisanal (ASM) and Small-scale (SSM) mining units in remote locations of the world, and Brazil is one of the main countries that has ASM and SSM on its territory. The present paper draws some definitions of Small-Scale Mining and Artisanal Mining, based on its productivity and its actual social and environmental implications, and of their sustainability. The analysis of production data of Small Scale and Large Scale Mining on global scale and on Brazilian scale shows the high potential of SSM in dealing with lower mineral grades and market fluctuations, due to its high flexibility. A general growth of the role of SSM in precious metals production in the next decades is foreseen. An elaboration on world ASM data led to a clear correlation between efficiency in production and an index of human development; this result is shown and discussed. Based on the potential of SSM to attend to the mineral market needs, efficiency in productivity is finally proposed as the main path to turn an ASM unit into a sustainable and profitable Small-Scale industrial extractive unit.

Technical and operational aspects of tunnel rounds in artisanal underground mining

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.

An Innovative Approach to Mine Blast Fragmentation Management Using Complexity Analysis: Three Case Studies

This paper introduces an innovative solution for devising a robust blasting plan that will present consistently good fragmentation performance under highly uncertain environments. The analysis will be carried out using complexity analysis tools, a model-free approach to complex systems which is particularly well suited to the problem of finding non-deterministic dependencies between multiple variables. The study is backed-up by data from over 2,000 blast records from Brazilian mines and identifies what are the critical aspects of the system and how to manage the blasting plan to reduce their impact on its performance.

Remarks on Some Mechanical Small-Scale Tests Applied to Properties of Materials

The paper presents the results of test campaigns on small-scale strength properties (particularly, micro-hardness) performed on two homogeneous materials: calcite, a very common and widespread mineral that is characterized by its relatively low Mohs hardness and its high reactivity with even weak acids; and glass, an amorphous solid characterized by the absence of the long-range order which defines crystalline materials. After a synthetic description of the principles underlying two of the three classical comminution laws, known as Kick’s law and Rittinger’s law, experimental results are discussed. The results of the tests performed show that both scale effect and size effect contribute to the non-constancy of mechanical properties at small scale for crystalline materials. On the other hand, for amorphous materials, a theoretical law considering size effects gives considerably different results from empirical measurements. Considerations and an extended discussion address these findings.

Evidences of the influence of the detonation sequence in rock fragmentation by blasting – Part II

This paper shows the work conducted at the Experimental Mine of the Research Center of Responsible Mining of the University of Sao 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.