T.O.E.’s Production of Paraiba
T.O.E.’s Paraiba Tourmaline deposit is such that we mine three different kinds or types of ore using several different mining techniques. All three types of ore, colluvial, alluvial, and pegmatite, contain varying amounts of tourmaline crystals including the brilliantly colored Paraiba tourmaline. True Paraiba tourmaline, cuprian-elbaite tourmaline, is extremely rare even at the Paraiba deposit. For every gem-quality blue Paraiba found, there are over 20 dark-green tourmalines and more than 200 black tourmalines recovered.
Over the millions of years since the Paraiba deposit was formed on Serra da Frade, weathering and erosion has combined to form two types of ore. First, there is the colluvial ore—this is material that has weathered out of the pegmatites, but is essentially in-place plus other in-place debris. Between 2 and 3 meters of this type of materials covered the entire surface area of Serra da Frade. Secondly, alluvial deposits were formed in ancient and modern drainage channels.
Colluvial ore was removed from Serra da Frade using heavy equipment and trucks. It was stockpiled awaiting processing through the tourmaline recovery plant. The removal of the colluvial exposed the surface outcrops of four tourmaline bearing pegmatites. (Locally, the pegmatites are called “lines”) One of these “lines,” Line #4, presented an opportunity to mine a significant tonnage of in-place “line” material.
A number of tourmaline bearing “lines” are present on T.O.E.’s property on Serra da Frade, and alluvial mining operations have discovered additional “lines” on the flat approaches to Serra da Frade. The “lines” are mined either by miners using hand tools or mechanically mined using hydraulic excavators.
.The “lines” are hand-mined from the surface downward, from adits driven into the mountain side or from mining accesses off of vertical shafts. “Lines” that are hand-mined are those that are too narrow at the surface to mine using mechanical equipment, have been mined to a depth greater than the hydraulic excavator can reach or ones that are not accessible from the surface.
The “line” known as “Line #4” has a very large surface cross-section at the outcrop on T.O.E.’s property. Line #4 was mined to a depth of between 10 meters and 20 meters using a hydraulic excavator. The line material was loaded into trucks and hauled to an ore stockpile area. This material will be screened and washed to recover any tourmaline. During the mining a number of tourmaline crystals were recovered along with minerals that indicate the possible presence of “pockets.”
T.O.E. has identified three alluvial deposits at the mine site. Alluvial deposits are associated with a “modern” river, an “ancient” river, and a major structural trap at the breach in the bordering mountains. Sampling indicates that all three of the alluvial deposits contain Paraiba tourmaline of economic significance.
The “modern” river is the drainage that currently removes water from the largest portion of the greater mining area. It is an intermittent drainage that carries water only during periods of heavy rain fall or when water is discharged into the drainage basin during the washing of tourmaline bearing material. During the late 1980’s and early 1990’s more than a dozen washing stations were constructed along the course of this drainage as it meanders through the native cashew trees. The course of this drainage is well defined, as is the location of the historical washing stations.
Alluvial tourmaline is present in the “modern” river for two reasons. First, the historical washing stations located on the drainage used varying size screens and therefore, all tourmaline smaller than the capture screen were released into the drainage. Secondly, every time it rains, additional material is washing into and deposited in the drainage, and part of this new material is tourmaline. A number of truck load sized samples from this drainage were processed through the washing plant and the tourmaline content characterized. Some mechanical mining with excavator and trucks was completed, but the majority of the “modern” river alluvial is still in-place.
For millions of years water flowed from the majority of the Paraiba “lines” area by way of a meandering, braided drainage system that T.O.E. refers to as the “ancient” river. The “ancient” river alluvial deposit varies from a few 10’s of meters wide to more than 100 meters, and the thickness of the deposit varies from a few meters to 10’s of meters. The “ancient” river is about one kilometer in length. The simple math indicates the large size of this alluvial deposit.
Currently, all of T.O.E.’s Paraiba production is from the mining and processing of alluvial ore from the “ancient” river. The material is mined using a hydraulic excavator and either directly loaded into haul trucks or stockpiled for later loading into trucks by the company’s front-end loader. Depending upon the mining production rate and the amount of material being run through the processing plant, the material is trucked directly to the plant for processing or is stockpiled for future processing.
T.O.E. has constructed a state-of-the-art processing plant that is capable of treating 50 to 70 truck loads of ore per day. The multi-grizzly, multi-screen, multi-washing systems plant has variable speed ore feed and gemstone sorting conveyor belts.
A dual-deck grizzly removes all material greater than 50-millimeters in size with material smaller than 50-millimeters going into an ore storage bin. From the ore storage bin the material is moved to the screening system by a variable speed ore feed conveyor belt.
The screening system contains both a wet and dry screen. The waste material from the dry screen is removed using a conveyor belt and the ore from the dry screen is fed into a washing box and from the washing box onto a wet screen. The waste from the wet screen moves by gravity feed to a sediment collection box and then to the tailing water pond for reuse. The ore from the wet screen is fed onto two sorting belts where the tourmaline is recovered.
T.O.E. employs more than 30 people to mine and process about 500 tons of ore per day. They own and operate a hydraulic excavator, a large capacity front-end loader, several trucks, a fuel and service wagon, and a new, well constructed processing plant. All of this equipment and personnel work diligently and at no small expense to produce one large, high-quality Paraiba per day, or sometimes one large, high-quality stone per week or per month. Even with the best planning and well managed operations, Paraiba tourmaline is extremely rare and is expensive to recover.