XA9745125 A REVIEW OF SPANISH URANIUM RESOURCES AND RECENT DEVELOPMENTS IN THE PROVINCE OF SALAMANCA
J.A. GONZALEZ GRANDA, J. RUIZ SANCHEZ-PORRO, J. ARNAIZ DE GUEZALA FE Mining Centre, Salamanca, Spain
Abstract
Uranium exploration activities in Spain carried out during the 1950-1992 period, led to the discovery of a number of deposits in different geological environments. Presently there is only activity at the FE area in Salamanca province, where the only remaining mining centre is located. A new dynamic leaching processing plant with a capacity of up to 950 t U3Og t/year began operation in 1993, at FE mine. The development and planning of the mining in the open pits of ENUSA (province of Salamanca, Spain) under the present low market prices, has led to the implementation of a working scheme, based on the following concepts: Detailed knowledge of the distribution and quality of the mineralization by sufficiently close spaced drilling, with 3D positioning and grade estimation by deviation and gamma ray probing. Use of either geostatistical or arithmetical grade interpolation techniques, properly validated with production, adapted to the density of the information available. Economic optimization of the open pit, by means of the 3D Lerchs-Grossmann technique, as a guide for the final pit design. Calculation of the optimal pit shapes and recoverable resources under different price conditions. These techniques implemented by means of computerized data acquisition and processing systems, are used to face with versatility, the present economic conditions. A full review of the uranium deposits in the province of Salamanca is being carried out with these means.
1. URANIUM DEPOSITS AND EXPLORATION IN SPAIN
1.1. Historical exploration in Spain
Uranium exploration in Spain was carried out, from 1950 to 1981 by the Junta de Energia Nuclear (J.E.N.), a public organism that depends on the Industry Ministry.
The Empresa National del Uranio S.A.( ENUSA) created in 1972, is a company owned by the J.E.N. and the National Industry Institute (I.N.I.) (Fig. 1). ENUSA has carried out uranium exploration in Spain and overseas, directly, since 1974 until 1992, when all exploration activities were stopped and all the investigation effort was concentrated on the development and feasibility studies of the FE area deposits.
From 1989 to 1994 a Joint Venture, ENUSA/CISA (COGEMA), has done some exploration in the province of Caceres (precambrian/cambrian schists and hercynian granites), without outstanding results.
1.2. Uranium deposits
During this time, most of the favourable geological units of Spain have been covered with airborne and ground exploration methods (Fig. 2).
61 INCORPORATED IN 1972
ACTIVITIES
-PROCUREMENT OF ENRICHED URANIUM •PRODUCTION & EXPLORATION OF URANIUM CONCENTRATES -DESIGN & FABRICATION OF FUEL BUNDLES
PRODUCTS -ENRICHED UF6 FOR SPANISH REACTORS -DESIGN & FABRICATION OF FUEL BUNDLES FOR SPANISH AND EUROPEAN REACTORS
SHARE CAPITAL: 10.000 MILLION PTAS
SHAREHOLDERS TENEO: 60% CIEMAT: 40%
TOTAL WORK FORCE : 703 EMPLOYEES
CORPORATION'S INTEREST IN EURODIF (11,11 %) CORPORATION'S INTEREST IN COMINAK (10 %)
FIG. 1. ENUSA.
62 AIRBORNE
;£v£Xj GROUND
FIG. 2. Areas covered with airborne and ground exploration methods.
63 0 DON BENITO (Bada|oz)
AREA TYPE IN SITU RESOURCES PRESENT SITUATION (tU3O8)
CIUDAD RODRIGO VEIN 36i391 MINING / DEVELOPMENT (Salamanca Province) (IBERIAN TYPE)
VEIN UNDEVELOPED CACERES PROVINCE (IBERIAN TYPE) 1.082 NOT FEASIBLE PRESENTLY
DON BENITO VEIN UNDEVELOPED (Bada|oz Province) (IBERIAN TYPE) 3.225 NOT FEASIBLE PRESENTLY
MAZARETE UNDEVELOPED (Guadala)ara Province) SANDSTONE 5.666 NOT FEASIBLE PRESENTLY
TOTAL 46.364
FIG. 3. Uranium in situ resources in Spain.
64 GEOLOGY Tertiary basins. Mesozoic. Paleozoic rocks at green schists and lower metamorphic grade ^| Calc-alkalic rocks a)gabbro and
diorite , ultramatic (Betic range)
y} Two mica granites.
1 BETIC RANGE.S.Sir. 2 OSSA- MORENA ZONE. 3 SOUTHPORTUGUESE ZONE 4 CENTRALIBERIAN ZONE 5 MAFIC AND ULTRAMAFIC MASSIFS. 6 CATALANIDES
200 280 Km.
ON FIG. 4. Geological setting of uranium deposits in Spain. Geological setting and in situ resources are given in Figs 3 and 4. Among the great number of occurrences studied, a number of deposits were evaluated, some of them (vein type in granites of Caceres and Jaen) mined out by J.E.N.. Of remaining deposits the most important are in Salamanca where they are being mined, whereas the rest is not mineable under the present economic conditions.
The main deposits outside the province of Salamanca can be summarized as follows:
PROVINCE NAME OF DEPOSIT GEOLOGICAL TYPE IN SITU SETTING RESOURCES (t U3O,) Fluvial sandstone GUADALAJARA MAZARETE braided channels SANDSTONE 5 660 Triassic (Buntsandstein) Silurian BADAJOZ DON BENITO AREA carbonaceous VEIN (Iberian) 3 225 schists, in TYPE contact with granites ACEHUCHE- Precambrian CACERES CECLAVIN Cambrian VEIN (Iberian) 1 082 schists, in TYPE contact with granites
Most of the in situ resources (78%) and all the presently mineable resources of Spain, are located in the province of Salamanca.
RAR resources amount to 9148 t U, and EAR-I to 10 688 at the < $80/kg U cost range. Average grades range from 0.6 to 2 kg/t, depending on the cut-off grades (from 0.2 to 1.0 kg/t).
The main deposits in Salamanca are of the vein-Iberian type, with mineralization placed in fractured precambrian- Cambrian and occasionally Silurian schists (map in Fig. 5). The deposits are of a low temperature hydrothermal origin. The main metallogenetic characteristics are summarized in Fig. 6.
The mineralization controls at regional and ore body scale are:
1) Regional fracture zones NE-SW; 2) Ore deposited in associated (Riedel type) fractures, following complex patterns; 3) Ore in a band parallel to the pre-tertiary erosion surface, 5-20 m below and deposited in the reduction zone and lower part of the oxidization zone. 4) Occasional lithological control, when carbonaceous schists and contrasts of competence (hardness) are present.
A block diagram is given in Fig. 7, and a map of mineralized fractures at FE in Fig. 8.
1.3. Historical uranium production
The evolution of the production in Spain, is summarized in Fig. 9.
Production sites at different state of activity are shown in Fig. 10.
66 A A A A A A A A A A A A A A A A A AAAAAAAJ A A A A A A/"" \i A A A A A A A A A A A A A A A A A
GEOLOCY SIZE OF DEPOSIT PRESENT STATE
0 - MC t,]0> o GEOLOGICAL EVALUATION O 500 - JOOC I UW COUPLETH) EVALUATION 3.000 - 5 ooc t JJOS UN0CVO.0PED PRCCAMBRUN - CAMBRIAN o SCHISTS O OEVELOPMEHT / MININ0 0 1000 2000 MOO 4000 5000 Mts. SCALE D • URANIUM OCCURRENCE Rcf.: CCOINGCR.DWC
FIG. 5. Geological map with the main uranium deposits in FE area (Salamanca).
67 1 •- High geochemicai U Content in the carbonaceous schists.
2.- Nature of the alteration processes: Chloritization and hematitization (intensive but not penetratives).
3.- Low temperature, hydrothermal, paragenesis.
4.- Banded, geopetal andvarved structures; Subsurficial environments and intermittent character of the mineralization.
5.- Radiometric age of the pitchblende (37 - 57 m.a., lower tertiary).
6.- Temperature (70 - 230°C) and salinity (0 - 25% NaCI) deducted from fluid inclusion studies.
7.- Primary ore placed in fractures and breccias.
8.- Surficial character of the tectonic processes.
FIG. 6. Metallogenetic characterization of FE type uranium deposits.
68 Tertiary arkoses
Precambrian • Cambrian Schists
Mineralized Zone (in fractures)
Oxidized Zone
Uranium mineralization
Radioactive anomaly In surface
FIG. 7. Uranium ore controls at FE area (diagram).
69 FIG. 8. Mineralized fractures at Fe mine.
70 t U3O8 350
301 300 - 270 263 260 254 254 250 237 225 230 219 216 207 200 - 183 165
150 140 127 132 128 132
100 86
50 -
0 - i r 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94
0 ELEFANTE E3i-A HABA • QUERCUS
FIG. 9. Historical evolution of uranium production in Spain. FR ANC1 A
LEGEND
IH MILL UNDER OPERATION
jf| NOT OPERATING MILL SITE % UNDERGROUND MINE O OPEN-PIT M3NE ^ HEAP LEACHING
+ TAILINGS STORAGE
B : DECOMMISSIONED
C : ON DECOMMISSION STILL IN OPERATION OR PROJECT D : UNDER OPERATION; DECOMMISSIONING
FIG. 10. Uranium facilities in Spain. 2. PRESENT ACTIVITIES
2.1. Exploration/development
2.1.1. General
Presently, all investigation related activities are concentrated in FE area, province of Salamanca, where development drilling at 10 x 10 m spacing, is being carried out at a rate of 100 000 m of percussion boreholes per year. In Fig. 11 all exploration and development drilling in recent years is shown compared with in situ resources.
Great effort is being made to complete the investigation of the D and M-SAGERAS deposits close to FE (Fig. 5), from which all medium to short term production will be obtained, together with FE.
2.1.2. Implementation of new integrated data acquisition and processing techniques to investigation by close spaced drilling, open pit design and mine planning
In the present situation of low market prices for the concentrates, it becomes very important to reduce production costs. The first step is to have the best possible knowledge of the deposits, so to be able to plan accurately the mining operations. This affects the following aspects:
grade and tonnages forecast,
localization of ore,
localization of barren areas in or nearby the deposit, to place waste dumps, in order to reduce transport distances,
design of haulage roads,
determine types of ore that need different processing parameters.
The acquisition/processing system at FE is shown in Fig. 12.
To achieve this, ENUSA has upgraded the following phases of the process:
2.1.2.1. Grade estimation by simultaneous gamma ray and deviation logging
In the FE type deposits, due to the foliated and fractured nature of the schists, borehole deviation can be of importance at the 10 x 10 m grid scale (Fig. 13). To correct this, boreholes are logged systematically with simultaneous gamma scintillometric and magnetometric deviation probes. Position and radiometry is recorded every 10 cm.
Great care is taken regarding the regular calibration of probes, correction of background (most due to Rn), and water absorption (see Fig. 14). Grade is estimated through the application of correlation curves, specific for each deposit. The whole process is computerized.
2.1.2.2. Ore body grade modelling by geostatistics and other methods
All borehole data is stored in a workstation with the processing programs. Due to the irregular distribution of the ore, geostatistics are only used in the wide spaced data, whereas average within
73 surface of influence, has proved to be more accurate, with data from the 10 x 10 m grid. This fact can be seen taking the example of an area in FE, comparing data from kriging and average with production (Fig. 15).
2.1.2.3. Economic optimization of open pit design
Economic optimization and analysis is done systematically on all deposits, as a guide for the final pit design. Three dimensional Lerchs-Grossman optimization techniques, implemented through the WHITTLE-4D software, are used.
Bearing in mind the present economic situation, ENUSA tries to mine its deposits as economically as possible and to maintain open the possibility of future exploitation of lower grade ore, not mineable today.
When deciding the optimum pit for the price considered (Fig. 16), the pit with the maximum net present value (N.P.V.), is initially chosen. As the N.P.V. curve is normally quite flat in its maximum, and if the pit permits a convenient scheduling of the mining operation, a bigger pit can be chosen if trying to increase the recoverable resources, or a smaller one if the scheduling is difficult, without much change in its economic value.
In short the priorities for ENUSA are:
Design a pit that will produce the maximum economic value.
Design a pit that, once mined out, permits, if economic conditions improve, mine the remaining, lower grade ore (nested optimum pits).
Schedule the mining operation looking for short distances to dumps but without dumping waste over lower grade ore zones, mineable at reasonably higher prices.
2.1.2.4. Estimation of recoverable resources at different economic conditions
Using the same techniques, a range of optimum pits for different prices can be obtained (Fig. 17). This curve is valid as far as the level and distribution of costs does not change significantly, that is, the mining and treatment methods do not change.
2.2. Production
In 1994 production was started at D mine, simultaneously with FE. Treatment of the ore is done at the Quercus Plant (Fig. 18), that was commissioned in 1993. The plant uses a mixed dynamic-heap leaching process. One characteristic of the FE ore is that uranium gets concentrated in the fine grained material. The ore is sorted at the following sizes:
> 10 mm Waste (67% tonnes; 15% U3Og) 1 mm < x < 10 mm Heap leaching (22% tonnes; 20% U3Og) < 1 mm Dynamic leaching (11% tonnes; 65% U3Og)
The treatment is acid leaching, with solvent extraction and precipitation with ammonia. The capacity of the plant is 950 t/year, being the present production level of 300 t/year.
74 METRES ! U308 (Thousands)
1982 1983 1984 198S 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 YEAR
EXPLOR. SALAMANCA 0 DEVELOP. SALAMANCA 0EXPLOR. REST SPAIN HiN SITU RESOURCES
FIG. 11. Exploration and development drilling. DEVELOPMENT BOREHOLES
GEOSTATISTICS OTHER TECHNIQUES
EXPLORATION 3D BOREHOLE 3D GRADE OPEN PIT OPTIMIZATION BOREHOLES DATABASE (BLOCK) MODEL (X,Y,Z, GRADE, THICKNESS^ 3D OREBOOY FINAL OPEN PIT (+ROAD AND DUMP) GEOLOGICAL MODEL DESIGN DATA 3D TOPOGRAPHIC 3D TOPOGRAPHIC DATABASE MODEL ECONOMIC TOPOGRAPHIC MINING ANALYSIS DATA CAD TECHNIQUES
- LONG TERM PLANNING; LIFE OF DEPOSIT
- MEDIUM TERM PLANNING; ANNUAL
- SHORT TERM PLANNING; MONTHLY (PRODUCTION, BLASTING)
FIG. 12. Diagram of borehole data acquisition/processing at FE. X = 410 Y = 1710 Z = 560
450 640 640
630- -630
620- -620
610 -610
600 -600
590- -590
580- -580
570- -570
560 560
FAULT BRECCIA F8ADI0METRIC GRADE: = 3%o (Apparent dip of fault)
-0 FIG. 13. Borehole profile from D Mine. oo
— BOREHOLS Li>6i)INQ 3D POSITIONNING CORRECTIONS: PERCUSSION DRILLING - WATER BOREHOLE RADIOACTIVITY (cps x m) COST: i 8 S/m (90%) • BACKGROUND DATABASE WIDTH • PROBE CALIBRATION
CORRELATION CURVE . f '•>••,- HAOIOACTIVITY / 0R4DC DIAMOND DRILLING COST: ±80 $/m (10%) CUTTINGS FROM PERCUSSION DRILLING
REAL TIME COMPUTER PROCESSING OF BOREHOLE DATA
J- 1 t 1 QEOSTATISTICS • , t "1 I1" OPTIMISATION, PIT DESIGN >:\ MINE PLANNING TOP { 1 t t lt,i ;
FIG. 14. Grade estimation by gamma ray logging. (50 x 50 m) METHOD: EXPLORATION GRIDS / INVESTIGATION (20 x 20 m) KRIGING
METHOD: DEVELOPMENT / GRIDS PRODUCTION (10 x 10 m) AVERAGE IN SUFACE OF INFLUENCE
COMPARISON PRODUCTION BENCH 618-624 (FE)
ORE (t) GRADE (Kg/t) 0308
PRODUCTION 77.247 0,480 37.046
AVERAGE 83.267 0,453 37.696
KRIGING 60.639 0,391 I 23.688
FIG. 15. Comparison of kriging with average at FE. 00 ORE (miiiion t) o N.P.V. (billion PTA) U3O8 (Thousands t) 4 5
3 —
— 2
— 1
o — 2517747 4496638 5652285 9449878 23599989 TONNES OF ROCK
iORE CDU3O8 ""-BEST N.P.V.
(*) Selected Pit
FIG. 16. Optimum pit for current price. Millions U3O8 (Thousands)
3000 4000 5000 6000 7000 8000 9000 10000 SELLING PRICE
FIG. 17. Recoverable resources versus price curve. oo ORE + WASTE EXTRACTION
RADIOMETRIC ARC | WASTE I I SELECTION I——1 WASTE DUMP I
ORE
CRUSHING < 100 mm.
FIRST WET GRINDING l»iomm.
SECOND WET GRINDING
ACID LEACHING HEAP LEACHING
COUNTER CURRENT DECANTATION WASHING
CLARIFICATION
EXTRACTION
STRIPING
TAILINGS PRECIPITATION + FILTRATION NEUTRALIZATION ]|
TAILINGS DAM DRYING + PACKAGING
URANIUM CONCENTRATE
FIG. 18. Flow diagram of the Quercus Plant.
82 2.3. Decommissioning
The Andujar Plant was decommissioned by ENRESA (Spanish Radioactive Waste Disposal National Company), ending in 1993. Decommissioning of the LOBO-G plant in La Haba Mining Centre by ENUSA is scheduled to be completed in 1995. Within the Saelices Mining Centre (FE mine), the old ELEFANTE plant is being, presently, decommissioned.
BIBLIOGRAPHY
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ARNAIZ DE GUEZALA, J., RUIZ ESTEBAN, B., RUIZ SANCHEZ-PORRO, J., Update of Uranium Resources in Spain, U deposits in the Salamanca province, Technical Committee Meeting on uranium resources and geology in Europe, Marianske Lazne (Czechoslovakia) (1989).
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83 SERRANO PILLET, J.R., ARTIEDA GONZALEZ-GRANDA, J., Aprovisionamiento de concentrados de uranio para las centrales nucleares en Espana, Proyecto Quercus, VIII Congreso Internacional de Mineria y Metalurgia, Oviedo (1988) t-II, 356-376 (in Spanish).
84