Overview
Stage | Preliminary Economic Assessment |
Mine Type | Open Pit |
Commodities |
|
Mining Method |
|
Processing |
- Sulfuric acid (reagent)
- Heap leach
- Agitated tank (VAT) leaching
- Counter current decantation (CCD)
- Carbon in column (CIC)
- SART
- Cyanide (reagent)
|
Mine Life | 10 years (as of Jan 1, 2017) |
Source:
p. 8
Company | Interest | Ownership |
Calibre Mining Corp.
|
7.5 %
|
Indirect
|
Rosita Mining Corporation
|
17.5 %
|
Indirect
|
Century Mining S.A.
|
75 %
|
Indirect
|
In October 2018, Calibre and Rosita Mining Corporation entered into a joint venture agreement with Century Mining S.A., for further development and advancement of the project. In consideration therewith, a new Nicaraguan joint venture entity, “Santa Rita Mining” was formed, in which Century will acquire a 75% interest and Rosita and Calibre will acquire a 17.5% and 7.5% equity interests, respectively. Calibre and Rosita transferred all technical know-how relating to the Rosita District Project to Santa Rita Mining and Century committed US$8.5 million to fund the construction, commissioning and operation of a processing facility to treat the Santa Rita stockpile resource on the project in order to earn its 75% joint venture interest.
Summary:
Deposit Types
The main types of deposit on the Rosita property are Cu-Au-Ag skarn at Santa Rita, R-13 and Tigre Negro, Fe-Cu-Au skarn at Magnetite Hill and Cu-Au-Ag porphyry at Bambana(Tipispan and T3 area). The skarn deposits are characterized by calc-silicate metasomatism, retrograde alteration and silicification. The porphyry copper mineralization at Bambana is characterized by propylitic, silicic and potassic alteration.
Skarn deposits form through the physical and chemical reaction between igneous rocks intruded into calcareous sedimentary rocks.They occur adjacent to (exo-skarn) or within (endo-skarn) an intrusive body. Emplacement of the intrusive is controlled largely by transfer structures in the back-arcbasin as well as splays along arc parallel structures in the magmatic arc environment. Alteration zoneis controlled by the temperature gradient and is overprinted by metasomatic and retrograde alteration. Mineralization is commonly vertically zoned from chalcopyrite-magnetite to chalcopyrite-bornite-gold-pyrite to pyrite-chalcopyrite. The copper-gold-silver deposit at the Santa Rita pit is examples of skarn mineralization.
The targets of this resource study are tailings and six historical low grade stockpiles around the Santa Rita pit.Each stockpile (North, Northeast, East, South and Southwest) was named based on the direction to the Santa Rita Pit. RST believes the stockpiles were originally derived from Santa Rita pit.
Based on P.A. Bevan reporting, during the production from Santa Rita mine, material containing less than 2% copper was stockpiled. All the stockpiles are mixtures of oxide and sulphide materialsand from clay to bouldersize. The ore minerals are mainly malachite, chalcocite and chalcopyrite with some azurite, chrysocolla, chalcanthite, tenorite, cuprite, native copper and native gold.
Mineralization
Santa Rita pit
The Santa Rita pit is a skarn type Cu-Au-Ag deposit(Bevan, 1973). The marble, garnet and epidote skarn rocks have been formed by the metamorphism of interbedded Cretaceous sediments of calcareous and siliceous nature and andesitic volcanics. The metasomatism was brought about by Tertiary intrusions, mainlydiorite and monzonite. The regional strike is approximately northeast.
The main mineralization lies on the southern flank of a small dioritic intrusion. In the mine the favourable garnet skarn horizon is about 152m thick, strikes easterly and dips 50 degreesto the southeast. It is underlain by altered diorite and overlain by chloritized andesites and calcareous tuffs. Intenselime, potash and siliceous metasomatism have altered the calcareous sediments to marble or to garnet-quartz-calcite-epidote-orthoclase-pyriteskarn. The interbedded volcanic and andesitic and dioritic dykes have been altered in many cases to epidote skarn and in others to siliceous skarn.
Garnet skarn is the host rock for the mineralization. Red, brown, yellow and green varieties of garnet are present. The mineralization zone occurs as lenses, pods and stringers of massive sulphides in well-fractured or brecciated skarn. There is commonly more chalcopyrite than pyrite. Massive pyrrhotite occurs in one zone onthe north side of the pit near the footwall. Gold valuesare localized by a north-northwest-trending fault.
In the central part of the pit there is a quartz-garnet skarn breccia zone with finely disseminated pyrite and chalcopyrite. The garnet is chiefly red or red-brown.The zone itself might be a breccia pipe of the Cananea type. In the east end of the mine the garnet skarn is mainly composed of the yellow variety, particularly adjacent to bands or masses of marble. The mineralization may be disseminated or massive chalcopyrite, often associated with chlorite, magnetite, pyrrhotite and pyrite. It may also occur as lenses or veins of quartz-chalcopyrite-pyrite.
The mineralization zones appear to have been localized in part by two major fault systems: (a) north-northwest-trending shears and quartz stringers and replacement zones with steep dips; and (b) northeast-trending shear zoneswhich offset the north-northwest faults. Stubby east-west breccia zones feather out from the northeast trending shears.
Capping the three primary sulphide zones were secondary enriched zones of chalcocite, dipping southwest, and oxidized zones composed principally of malachite. Other copper minerals noted include native copper, cuprite, azurite, chrysocolla, chalcanthite,coveIlite, tenorite and "grey coppers".
R-13 Pit
The R-13 Zone is a northeastern extension of the Santa Rita mineralized zone. The deposit contains copper, silver and gold concentrations in a northwest trending shear zone hosted exclusively within an intensely fractured and propylitized quartz diorite. The main hypogene minerals found in the drill cuttings, in order of decreasing abundance,are reportedas: quartz, pyrite, chalcopyrite and bornite. Pyrite in the R-13 deposit occurs as discrete grains in quartz-pyrite veinlets and in fracture zones containing massive chalcopyrite and quartz. Chalcopyrite is not as widespread as pyrite and is concentrated along the main northwest shear zone. Argentite is identified as the main silver mineral in the R-13 deposit. Gold in the fracture zones is closely associated with copper and silver. Drilling has shown that this relationship is confined to intervals of silicic alteration within a propylitically altered quartz diorite. This spatial association suggests that the gold was deposited during a late stage or completely separate hydrothermal event in the Rosita Fault.
Other Mineralization on Some Exploration Targets
A zone of a superficial supergene enrichment presentabove a porphyry-type Cu-Au-Ag mineralized monzonite intrusion at Tipispan area, which was encountered in trenches and drill holes.
T3 is a secondary copper mineralization zone on a south facing slope in the western part of the Rosita D Property. Historically this area had been subject to selective mining. Trenching, soil sampling, IP geophysical survey and drilling indicated the presence of an exotic copper deposit on the side of a hill.
Summary:
Rosita is proposing to reclaim the Stockpile and tailings at Santa Rita with the use of local construction contractors. Conventional earth moving equipment such as hydraulic excavators or front end loaders will be utilized. The nature of the “loose” stockpile and tailings mineralized material does not require any drilling and blasting activities. The reclaimed material can be transported to the mobile crushing plant via articulated or rigid frame haul trucks.
The location of the stockpiles and tailings are in close proximity to the mobile crushing plant, and proposed process facility via existing roads in and around the area. The project does not require any selectivity or detailed grade control however, selective reclamation of specific stockpiles will take place. It is anticipated that the higher grade North Stockpile will be reclaimed initially and this has been addressed in the early year cash flow presented.
The bulk of the resources from each stockpile will be focussed on the indicated resources. However, where inferred resources are at the edges of stockpile they will be excavated first and thus inferred and indicated resources will be mixed in the feed to the treatment plant.
From the sequence of mining planned, the grades used for the cash flow statement have been defined as:
- First 5 years: 0.65 g/t Au; 10.0 g/t Ag (for the mill) 8.0 g/t Ag (for the heap leach); 0.80% Cu;
- Second 5 years;0.47 g/t Au; 7.79 g/t Ag; 0.50% Cu.
As the total mineralized resource will reclaimed, there is no need to address waste handling or deposition of the same. Specific lower grade stockpiles will be reclaimed as dictated on the process economics at that time.
The loading and material handling costs has been shown in the operating cost section and is based on the following:
- Production required to the crusher from the stockpile –328,500 tonnes per year (years 1-3) and 657,000 tonnes per year (Years 4and after).
- Tailings –36,500 tonnes (Years 1-3) and 73,000 tonnes (Year 4 and after).
- Hours of Operation per day –16 hours. This requirement is flexible with the major requirement being the supply of feed to crusher based the production requirements.
- Bulk Density –Stockpiles–2.0, Tailings –1.82.
- Haul Distance to Mobile Crushing Facility –500 m. –1000 m.
The cost for the contractor includes equipment supply, manpower, diesel consumption, and required service lubricants.
This phase of the project can be performed by the local contractor and with minimal supervision from Rosita because of the no grade control requirement. It also allows for reclamation flexibility from the multiple stockpiles based on gold and copper grades.
Specific challenges in the reclamation of the Stockpiles and Tailings will be during the local rainy season. Excavation and hauling could be slowed due to the high clay content of the material. Increased haulage during non-rainy season could be scheduled to minimize any reduced production. This is also the case for the subsequent crushing and two(2) product stockpile for the process feed material. As mentioned previously, water diversion and control around the site will be important.
Flow Sheet:
Crusher / Mill Type | Model | Size | Power | Quantity |
Jaw crusher
|
.......................
|
|
165 kW
|
1
|
Impact crusher
|
.......................
|
|
250 kW
|
1
|
Ball mill
|
|
7' x 10'
|
200 HP
|
1
|
Summary:
Mobile Crushing
The two (2) stage mobile crushing plant will be strategically located around the Santa Rita site to ensure close proximity to the stockpile being reclaimed and also crushed product surge capacity for the mill circuit. Closeness to the heap pad will also be beneficial to allow blending and agglomeration of the mill leach residue.
The plant will have a nominal capacity of 250-300 mtph (metric tonnes per hour) of feed material to produce two (2) final products of +¼-in. (heap leach) and -¼-in. (mill feed). Power required for the system will be via a 1000 kw (kilowatts) diesel generator.
Stage 1 Mobile Jaw Crusher will consist of a feed hopper, 1300 x 4900 vibrating grizzly feeder, PE900 x1200 primary jaw crusher and associated discharge conveyors and mounted on a tri-axle road trailer. The connected power is 165 kw and is complete with all electrical components and cabling.
Stage 2 Mobile Impact Crusher will consist of a three(3) deck vibrating screen, PF1315 impact crusher, and associated return, discharge and product stacking conveyors and mounted on tri-axle road trailer. The connected power is 250 kw and is complete with all electrical components and cabling.
The sizing of the mobile system is large enough to minimize operating hours and operating costs, and allow for Year 4 ramp up in production.
Milling Circuit
The milling process facility will be located on the existing concrete slab area previously used for the copper recovery plant (1967). There will be no building required for the process area but an engineered containment will encompass the area to ensure no risk of contamination to the surrounding environment.
The feed material for the mill will be a mixture from the -¼-in. stockpile plus tailings loaded into a feed hopper/bin and discharged at a rate of 150 mtpd (6-8 mtph) (metric tonnes per day and hour). The feed to the mill will controlled by a weightometer and variable speed belt conveyor. Recycled cyanide process water will pulp the feed material directed into a 7-ft. dia. X 10-ft. –200 Hp modular ball mill. The ball mill discharge will be pumped to a hydrocyclone to ensure a P80 overflow sizing 75µm (80% passing 200 mesh). The cyclone underflow is closed circuited return to the mill. The mill circuit is standard design with SRL slurry pumps, pump box, launders, and sumps. Ball loading and sizing is designed accordingly. Leach feed pH will be controlled at 11 via the addition of slurried lime.
Processing
- Sulfuric acid (reagent)
- Heap leach
- Agitated tank (VAT) leaching
- Counter current decantation (CCD)
- Carbon in column (CIC)
- SART
- Cyanide (reagent)
Flow Sheet:
Summary:
The Santa Rita process facility will consist of following of the following circuits and include all associated pumping, piping, and electrical components.
- Stockpiles and Tailing Resource
- Mobile Crushing Plant to produce +1/4-in and -1/4-in material.
- Gold and Copper Heap–pads and ponds –agglomeration -conveyance
- Milling Circuit including ball mill, leach tanks, and thickeners.
- SART Circuit (Sulphurisation–Acidification –Recycling –Thickening)
- Carbon in Columns Gold Recovery Circuit to recover gold and silver from the SART and CCD mill circuits.
Gold and Copper Heap
The Stage 1 heap pad is designed to have a preliminary capacity of a total of three (3) years of feed material – 1.1 M tonnes. The pad will be designed to standard heap characteristics and will include excavation, compaction, geomembrane, LLDPE liner, over liner crushed material and all associated collection and drainage piping. The stage 1 pad area is 250 m. x 150 m ........

Operational Metrics:
Metrics | |
Plant annual capacity
| 720 kt * |
Daily processing capacity
| 2,300 t * |
Annual ore mining rate
| 730 kt * |
* According to 2017 study.
Reserves at March 6, 2017:
The Au cut-off grade for the resource estimate 0.3 g/t.
Category | OreType | Tonnage | Commodity | Grade | Contained Metal |
Indicated
|
Stockpiles
|
6,460 kt
|
Gold
|
0.47 g/t
|
96.7 koz
|
Indicated
|
Stockpiles
|
6,460 kt
|
Silver
|
7.32 g/t
|
1,521 koz
|
Indicated
|
Stockpiles
|
6,460 kt
|
Copper
|
0.5 %
|
32.2 kt
|
Inferred
|
Stockpiles
|
3,437 kt
|
Gold
|
0.46 g/t
|
50.3 koz
|
Inferred
|
Tailings
|
1,956 kt
|
Gold
|
0.56 g/t
|
35.2 koz
|
Inferred
|
Stockpiles
|
3,437 kt
|
Silver
|
8.66 g/t
|
957.5 koz
|
Inferred
|
Tailings
|
1,956 kt
|
Silver
|
9.65 g/t
|
607 koz
|
Inferred
|
Stockpiles
|
3,437 kt
|
Copper
|
0.61 %
|
21 kt
|
Inferred
|
Tailings
|
1,956 kt
|
Copper
|
0.21 %
|
4 kt
|
Mine Management:
Job Title | Name | Profile | Ref. Date |
.......................
|
.......................
|
|
Mar 6, 2017
|
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