Summary:
Deposit Type
Ulaanbulag deposit depends on the morphology of the mineralized region with shallow dip angle and variable thickness. Mineralization is defined by quartz-cali field cali-sericit-pirite alteration and low silica Au+As sulphide system associated. Ulaanbulag is oregon related gold deposit with its tectonic-macmic environment, its carbon dioxide components, and its geochemical properties.
Geology
In the area of Ulaanbulag deposit, Lower Paleozoic metamorphic-sedimentary rocks of the Shirguu Formation in the Kharaa region, Cenozoic sediments, and Middle-Late Ordovician intrusive rocks of the Boroogol Formation are found in this region.
The Ulaanbulag deposit is complex in terms of geological formation, and the sands of the Shirguu Formation scattered in the central part of the field formed an orebody extending latitudinally in the medium grained, inlaid, feldspar granite of the III phase of the Boroogol Formation in the upper part of the Ulaanbulag fault.
However, in the southern part of the deposit, a large massive of diorite of the Boroogol Formation phase I is found.
In the northern part of the field, several small orebodies of diorite were identified within the granite, occasionally around the boundary between granite and sandstone.
At several locations, the boundary between sandstone and granite is demarcated by the Ulaanbulag inclined fault and its branch faults.
In the geological cross-section, the granite containing orebody in the upper part of the section cuts the diorite found in the lower part, and along their boundary and weakened zone, the Ulaanbulag fault is mapped with a dip of 20-400 degrees southwest.
Mineralization
There are 2 main types of mineralization in the Ulaanbulag deposit. These include:
• Gold-sulphide;
• Gold-quartz vein type.
Two main types of mineralisation have been noted:
• A type of gold-sulfide. Gold-sulphide mineralization, which the majority of the deposit's gold reserves, is identified by beresite metamorphic zones. The gold grade is generally low, it has different distribution in different types of rocks, it is highly variable in small distances, and it has high variability of content. The gold content is directly proportional to the arsenopyrite or arsenic content, regardless of the density of quartz veins and veinlets, as in Boroo deposits. This type of mineralization is mainly contained in the Ulaanbulag fault and metamorphic granite rocks. In metamorphic sandstone and diorite xenoliths, the sulfide content decreases dramatically. This is why these less metamorphic rocks usually have lower gold content. The main sulfides in Ulaanbulag deposit are pyrite and arsenopyrite, and rare minerals such as chalcopyrite, galena, pyrrhotite, sphalerite, and dim ore are found.
• Gold-quartz vein type. Usually, the Ulaanbulag fault and its branches are found along the cracks and fissures, and there are fill veins, veinlets, and breccia-like veins with a thickness of several centimeters to 5 meters. The veins are low sulphide and sometimes contain visible gold inclusions up to 2 mm.
Alteration
Alteration In addition to boundary alteration, hydrothermal alteration zones related to mineralization are found in the deposit area. At the inner boundary of the granite, colored minerals are increased and grain size is observed, while at the outer boundary there is hornification and weak silicification, the containing sedimentary rock has become gneiss in the part cut by the granite apophysis. Along the Ulaanbulag fault and its branch faults and cracks, calcined, beresited and propylitic metamorphism zones are distinguished in the host rocks forming a belt formation. The intensity of transformation varies depending on the type of rock. Granite is highly metamorphic, while metasediments and diorite are poorly metamorphosed.
• Strongly brecciated and silicified metamorphic zone with quartz veins, veinlets, stockwork and diffuse mineralization. Along the Ulaanbulag fault, it occurs as a strongly silicified metamorphism zone with micelle-shaped quartz veins and schistose stockwork, usually 0.1-0.2 meters at the surface and increasing to 5 meters in thickness. In addition to pyrite and iron oxides, the quartz veins contain occasional visible gold. According to the results of the spot samples, the gold content in the quartz veins /0.01-3.0 g/t or more/ varies greatly, which indicates that the distribution of gold in the quartz is not uniform.
• The pyrite-sericite-silica metamorphism or beresite metamorphism alteration Ulaanbulag fault and its branch faults and fissures, usually in granitic rocks, and the thickness ranges from 0.2 to 40 meters. The surfaces follow the Ulaanbulag fault for more than 500 meters and form a wider metamorphism zone in the granite, and along its branch faults and fissures, small mesiallike bodies (exposed surfaces) are established in the western and eastern parts of the deposit.
• Propylitic Alteration
This carbonate-chlorite alteration contains poor mineralization at the margins of the beresited alteration and is widespread in all rock types. The facies only form a metamorphic zone 200 m long and 40-80 m wide in the western part of the deposit, mostly set in metasedimentary sediments and, to a lesser extent, granite. In this zone, the gold grade is very low and, in this sense, indicates the peripheral part of the mineralization.