Experiences from Experimental Mining in Brazil

The Experimental Mine (EM) of the Research Center of Responsible Mining of the University of São Paulo became the subject of investigation in a few years after its development ; it is an open-pit quarry currently exploiting marble and gneiss , used to produce industrial limestone and construction aggregates. It is a developing enterprise, dealing with the challenges of a technological upgrade from a small -scale operation to the characteristics of a medium -sized company. The Experimental Mine Project (EMP) was born to attend a double demand: to provide research and development (R&D ) support to a growing company and to provide experimental opportunity for a field of knowledge such as mining engineering that requires a large scale for its experiments. The main challenges of the EMP are related with the remaining small -scale mining features, such as large variety of equipment available, high level of operational flexibility, scarcity or absence of mine planning, being focused on daily operations. In such an environment, the first role of the EMP was to evaluate in a quantitative way the effects of unit operations over the whole mining process. The current excavation technique is by drilling and blasting. Many experimental campaigns have been conducted on site, with different purposes. One of the main research lines was to increase the productivity of the quarry by lowering production costs and improving the quality of the product, then optimizing the entire production cycle; the relationship between the unit costs of drilling and explosives were evaluated, as well as the link between the blast design and some factors affecting the downstream processing of the product. The paper describes the methods employed to conduct the research and the improvements to be pursued, with the due consideration to the influence and interference of the many parameters involved, from the rock-mass characteristics to the final products

The Music of Blasting

A common adage in the Explosives Industry goes by saying that "Blasting is not bombing". One of the key differences between the two employs of explosive energy lays in the same gap existing between the application of acoustic energy that differentiates noise from music: timing and the distribution of energization in time. While timing in blasting is widely accepted to influence blast induced vibrations, it is still not completely investigated when related to rock fragmentation and downstream benefits. This paper shows a research about this topic, developedon two phases: 1) test blasts at the Experimental Mine of the Research Center of Responsible Mining of the University of São Paulo; 2) development project for large-scale production blasts in an open-cast mine. The first phase of the research was performed attempting to increase the productivity of the experimental mine, 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 and a more appropriate initiation sequence were designed according to the principles of: i) decomposition of the blast; ii) taking advantage of the free surfaces to favor the movement of the blasted material; iii) simultaneous holes firing as far away as possible, to avoid undesired cooperation of charges that may induce the explosive energy to work with shear effect instead of producing fragmentation. The results show that the proper selection of delay timing leads to significant benefits for rock fragmentation, downstream processes and the quality of final walls. The second phase of the study was a research and development (R&D) project in an open-cast mine with the goal to achieve an average P80 of 300 mm (11,8”) in the run-of-mine (ROM) product without altering the existing budget. The project included several variables in the blast design that were not previously taken into account, such as the orientation of natural joint sets in the rock mass, specific energy of the explosive and firing sequence. The new blast design method considered the directions of natural joint sets and determined the drilling pattern and the firing sequence accordingly to favor the movement of the blasted rock along its preferential direction, to reduce its confinement. At the end of the project, it was achieved an average P80 of 304 mm (12”) in the ROM, 50% lower than the one at the beginning of the project. The final blast of the project showed a reduction of 3% of the drill and blast cost, employing the same powder factor and the same drill pattern size used at the beginning of the project. The results of this study show how blast performance is related to variables that are not contemplated in the most common design methods or fragmentation models: the firing sequence, the degree of freedom and the direction of movement in the blast

Influence of blasting charges and delays on the energy consumption of mechanical crushing

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 nd 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 rushing the rock, and ad-ditional 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

On the influence of the angles of breakage in the pull efficiency of tunneling by drill and blast

In tunnel excavation by drill and blast, the rate of advance per pull is the key aspect to the working site productivity, and therefore the economic profitability of the Project. One defines Pull as the advance length per blast along the tunnel axis, and normally one differentiates the design pull (as the drilled length according to the blast design) and the actual pull (as the actual excavated length after the blast). The pull efficiency is defined as the ratio between the design and the actual obtained pull. Previous studies conducted by the authors of the present work showed a lack of correlation between the pull efficiency with the most common parameters defining a tunnel blast design. The present work considers a new variable: the angle of breakage, define as the angle of the prism of rock of competence of a single blasthole. Considering this new variable, a trend of correlation is observable, suggesting that the pull efficiency is generally lower for wider angles of breakage within the blast pattern

Socio-technical study of small-scale gold mining in Suriname

Small-scale gold mining is Suriname’s main economic sector, producing about two thirds of the nation’s gold. Despite this, the sector is only very loosely regulated and most small-scale mining activities are informal. Surinamese miners are only a minority: the majority are Brazilian migrants, who have no right to the land and therefore have to pay a percentage of their production for land use. This study reports the findings of a field mission to small-scale mines in the region of Brokopondo reservoir. We document the technical aspects of small-scale gold mining in Suriname and contextualize this technology to social issues to identify links with cultural, political and sociological factors. Our findings show that informality and insecurity lead to a mine management culture that applies short-term solutions, such as cheap but polluting and inefficient technologies, and fails to produce stable, long-term mining conditions for clean, efficient technology and secure business planning. We conclude that the social context of the mining economy in Suriname strongly interacts with the technologies employed

Experiences from Experimental Mining in Brazil

The Experimental Mine (EM) of the Research Center of Responsible Mining of the University of São Paulo became the subject of investigation in a few years after its development ; it is an open-pit quarry currently exploiting marble and gneiss , used to produce industrial limestone and construction aggregates. It is a developing enterprise, dealing with the challenges of a technological upgrade from a small -scale operation to the characteristics of a medium -sized company. The Experimental Mine Project (EMP) was born to attend a double demand: to provide research and development (R&D ) support to a growing company and to provide experimental opportunity for a field of knowledge such as mining engineering that requires a large scale for its experiments. The main challenges of the EMP are related with the remaining small -scale mining features, such as large variety of equipment available, high level of operational flexibility, scarcity or absence of mine planning, being focused on daily operations. In such an environment, the first role of the EMP was to evaluate in a quantitative way the effects of unit operations over the whole mining process. The current excavation technique is by drilling and blasting. Many experimental campaigns have been conducted on site, with different purposes. One of the main research lines was to increase the productivity of the quarry by lowering production costs and improving the quality of the product, then optimizing the entire production cycle; the relationship between the unit costs of drilling and explosives were evaluated, as well as the link between the blast design and some factors affecting the downstream processing of the product. The paper describes the methods employed to conduct the research and the improvements to be pursued, with the due consideration to the influence and interference of the many parameters involved, from the rock-mass characteristics to the final products

The Music of Blasting

A common adage in the Explosives Industry goes by saying that "Blasting is not bombing". One of the key differences between the two employs of explosive energy lays in the same gap existing between the application of acoustic energy that differentiates noise from music: timing and the distribution of energization in time. While timing in blasting is widely accepted to influence blast induced vibrations, it is still not completely investigated when related to rock fragmentation and downstream benefits. This paper shows a research about this topic, developedon two phases: 1) test blasts at the Experimental Mine of the Research Center of Responsible Mining of the University of São Paulo; 2) development project for large-scale production blasts in an open-cast mine. The first phase of the research was performed attempting to increase the productivity of the experimental mine, 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 and a more appropriate initiation sequence were designed according to the principles of: i) decomposition of the blast; ii) taking advantage of the free surfaces to favor the movement of the blasted material; iii) simultaneous holes firing as far away as possible, to avoid undesired cooperation of charges that may induce the explosive energy to work with shear effect instead of producing fragmentation. The results show that the proper selection of delay timing leads to significant benefits for rock fragmentation, downstream processes and the quality of final walls. The second phase of the study was a research and development (R&D) project in an open-cast mine with the goal to achieve an average P80 of 300 mm (11,8”) in the run-of-mine (ROM) product without altering the existing budget. The project included several variables in the blast design that were not previously taken into account, such as the orientation of natural joint sets in the rock mass, specific energy of the explosive and firing sequence. The new blast design method considered the directions of natural joint sets and determined the drilling pattern and the firing sequence accordingly to favor the movement of the blasted rock along its preferential direction, to reduce its confinement. At the end of the project, it was achieved an average P80 of 304 mm (12”) in the ROM, 50% lower than the one at the beginning of the project. The final blast of the project showed a reduction of 3% of the drill and blast cost, employing the same powder factor and the same drill pattern size used at the beginning of the project. The results of this study show how blast performance is related to variables that are not contemplated in the most common design methods or fragmentation models: the firing sequence, the degree of freedom and the direction of movement in the blast

Making economically viable the exploitation by D&B in a quarry within sensitive, highly populated area

The paper presents the results of an experimental campaign carried out at the Sasso Poiano quarry close to Varese, northern Italy. The area is near a historic site, inhabited villages and a well-known lake, so that the use of explosive is subject to severe restrictions imposed by Italian standards. The exploitation is therefore carried out by blasting with low specific charge (PF=50 g/m3) to obtain pre-fracturing of the rock, which is followed by mechanical excavation through backhoe excavators. The goal of the study was to test new techniques for the expansion of the mine, to reduce the production costs and increase the efficiency of the site, maintaining the same level of production as previously achieved by standard bench blasting. The hypothesis to be tested was that of introducing new equipment able to ensure the productivity of the plant with lower operating costs and maintenance. 28 blast tests have been performed, with the aim of obtaining a site law suitable to describe the behavior blast-induced vibrations within the marlstone and therefore predict the maximum allowable charge per delay (CPD) to respect legal limits of peak particle velocity (PPV). Afterwards, 9 blasts were selected to evaluate two options: varying the CPD and/or the geometry of the drilling mesh. The grain size distribution of the blasted material was analyzed through a photogrammetric technique, to evaluate the best solution. The results determined the best blasting configuration, together with the purchase of a single backhoe excavator, smaller than those currently adopted. This choice reduces the fuel cost by about 40% and lowers overall costs of the equipment maintenance