Geology of Roşia Montană
Map of existing works of surface mining
Existing surface mining works: areas where the pits are proposed are heavily affected by existing surface and underground mining works. There are two pits – Cetate and Carnic and many waste stockpiles.
Map of existing underground mining works
Existing underground mining work: there is a volume of around 2 million m3 of underground mining excavations, which generates acidic waters in a natural and continuous way.
Exploration, geology and resources
Roşia Montană Gold Corporation implemented a vast exploration and research program regarding the deposit in Rosia Montana. The works mainly consisted in the plotting and furrow sampling of all the accessible underground mining works and all surface buttes. In parallel, an extensive geological research drilling program was conducted on the surface and in the underground. All the collected samples were analysed for gold and silver. Additionally, tests were conducted for another 47 elements, on a number of composite 1224 samples.
In addition to these works, a large number of metallurgical tests were done in labs from Canada and Australia, with a view to determining the best technological flow for preparing the ore from Rosia Montana. All the information thus obtained was used to build a model block of the Rosia Montana deposit, which includes about 29 parameters and was used to estimate resources and reserves.
Map of drillings performed by RMGC
To date, RMGC has performed 1170 geological research and geo-technical drillings, totalling 140,000 drilled meters. All the geological research drillings were sampled on each meter, and all the collected samples were analysed for gold and silver.
Map of furrow samples executed by RMGC
RMGC has collected 66100 furrow samples with a length of 1 meter, both from underground mining works and surface buttes. All the samples were analysed for gold and silver.
In Rosia Montana, 2 dacitic sub-volcanic bodies dating from the Neogene, named Cetate and Carnic, were intruded vertically in a sequence of Cretacic sediments, and then close to the surface, in a unit of polymictic breccias, called “vent breccias”. These were formed as magmatic-phreatic diatreme breccias, as a response to the raise of dacitic magmas in the complex.
Associated with the dacitic intrusives (both inside and along the limits of the intrusives), there are sub-vertical breccias columns, which, according to the latest interpretations, are diatremes. The northern and eastern parts of the complex from Rosia Montana are covered with lava and later andesite agglomerates, associated with the volcanic activity from Rosia Poieni.
The deposit from Rosia Montana is intensely altered from a hydro-thermal viewpoint, with a predominance of argilization, adularisation and silicification. The ore from Rosia Montana is gold-silver bearing, and mainly appears in a disseminated form, associate with pyrite. It also appears in the form of veins, placer deposits or associated with breccias bodies, cases in which free gold could also be found, but quite rarely. These areas, with higher gold contents, were intensely mined in the past. No other element analysed in Rosia Montana presents any contents that could be recovered in a cost-effective manner.
Geological evolution of the orenext prev
1. The formation of an explosion breccia body within sediments of Cretacic age was the first stage in the development of the structure from Rosia Montana. During the times of volcanic rest, sedimentation processes took place, which led to the mixed genesis (volcanic and sedimentary) of this formation.
2. Placement of the two dacites bodies – Carnic and Cetate (age about 13.60 million years) in the structure from Rosia Montana.
3. Continuation of the volcanic activities resulting in the formation of mixed breccia structures within the dacite bodies and the explosion breccias. Depositing of gold-silver bearing mineralisation – impregnations, veins, placer deposits (age about 13.17 – 12.71 million years).
4. Formation of the black breccia body between the two dacitic bodies – Cetate and Carnic. Last mineralisation phase: veins with carbonates, quartz and sulphides.
5. Formation of a post-mineralisation breccia structure in the southern part of the Rosia Montana deposit (age about 11 million years).
6. Placement of newer volcanic rocks, generated by the magmatic activity from Rosia Poieni, which covered and preserved the ore deposit from Rosia Montana (age about 9.42 – 9.16 million years).
Pits proposed for the Rosia Montana Mining Project
The deposit from Rosia Montana will be mined in 4 pits, the reserves being estimated at 214.9 million tons, with average contents of 1.46g/t Au and 6.9g/t Ag, representing 10.1 million ounces (314 t) Au and 47.6 million ounces (1480 t) Ag - in situ metals.