The 7 million tons of ore processed in the period 1968-1986 produced some 2 million m3 of coarse tailings and 1.2 million m3 of slimes. Of the coarse material some 700,000 m3 were sold for their use in road workings and as aggregates with 1.3 million m3 remaining on site.
In 1980-1982 Indumetal evaluated the old dumps and tailings ponds by sampling the dumps and slimes. Rioibex reviewed all the Indumetal data and determined there was considerable irregularity in the sample results from the slimes and confirmed the grade of the coarse dumps. A 1,000kg composite sample collected from various places from the tailings pond returned a grade of 2,835 ppm WO3.
In 1986, a company (Wolframexa) was formed between the Bonilla family and a regional government company to process the -3mm tailings from the current operation. The plant consisted in cyclones, spirals (LG7 and K67), and shaking tables. Tungsten recovery was reported to be of some 70% and Sn some 60%.
In late 2009, IRS sampled the coarse tailings dumps by digging 21 trenches with variable depths between 1 and 5.5 meters. 20 kg samples were collected at each site and sent for preparation and analysis to ALS Chemex lab.
In 2010, a detailed survey of the coarse tailings dumps showed a total volume of 1.2 million cubic meters equivalent to 2.5 million tons.
Pilot plant testing
A pilot plant testing is currently being undertaken by ERAL (a Spanish gravity concentration consulting firm) to assess the concentration on the fraction 0/2 mm tailings existing in the dumps of La Parrilla Mine. The test is carried out Rio Arimosan facilities (Avila province) where the original La Parrilla material was sieved at -2mm. The testing plant basically consists of the following elements:
1) Main Hopper equipped with belt feeder of variable speed to regulate the dosage.
2) Conveyor belt to feed the spiral plant.
3) Concentration pilot plant with pumping group, hydrocyclone and spiral.
The preliminary test undertaken on some 100 metric tons of tailings sieved to -2 mm showed excellent recovery of the scheelite with a good concentration rate. Representative samples have been collected from the feed, cyclone overflow, concentrate middlings and tailings from the spiral. Assay results of all the products are pending.
Several settings of the spiral have been tested all of them with good results.
A second spiral concentration was performed on concentrate from a first spiral passage giving a very good concentrate. A second batch of test will be carried out on 500 metric tons of tailings at Rio Arimosan facilities. The material will be wet sieved to +4, 4-2 and -2mm and the -60µ fraction removed by cycloning. All fractions and the feed will be weighted for mass balance.
The +4, 4-2 and -60µ fractions will be sampled for WO3 and Sn contents before being discarded for metallurgical balance. The 60µ-2mm fraction will be treated in the ERAL spiral plant.
This second test will allow us to define and optimise the industrial process to be followed for the treatment of the coarse tailings at La Parrilla.
The industrial plant final design and layout is subject to the final results of the pilot plant test.