Gold-REE Aktiuz-Boordu mining district, northern Tien Shan, Kyrgyzstan
|Location||International Geological Congress,oslo 2008|
|Holding Date||08 September 2008|
The Aktiuz-Boordu Mining District is located in the Northern Tien Shan in the eastern part of Kyrgyzstan. The region is characterized by nappe-folding structures and comprises strongly deformed Precambrian and Lower Paleozoic sedimentary, volcano-sedimentary, and metamorphic sequences. Metamorphic rocks are represented by crystalline schists, para- and orthogneisses, marble, migmatite, amphibolite and eclogite lenses. These rocks are thought to be the oldest in the Northern Tien Shan (2,780 Ma).
Available U-Pb zircon age data for the Kemin Group migmatites yield ages of 2,200±50 Ma. Based upon their geological setting, multistage metamorphism and isotopic ages of retrograde metamorphism (1.1-1.9 Ga). The Archaean and Paleoproterozoic basement metamorphic rocks contain mineralization of various ages and types, including porphyry Cu, Au-sulphide, Au-Bi, barite, epithermal base metal and Au-Ag, REE and rare-metals. Two ore fields have been identified within the Aktiuz-Boordu Mining District, they are:
1) Taldybulak-Boordu, with Au, base metal, and porphyry Cu systems; 2) Aktiuz, with REE, Nb, Ta rare- and base metal deposits.
Rock types in the Taldybulak-Boordu ore field mainly comprise chlorite-amphibole and amphibole schists, amphibolites, and migmatites of the Paleoproterozoic Kuperlisay suite. The younger Paleoproterozoic suites are represented by mica schists and granite gneisses, which are separated from the Kuperlisay suite by a fault.
The basement rocks are cut by a complex network of Paleozoic sub-volcanic intrusions, accompanied by eruptive rocks and breccia pipes. These represent the root system of Middle and Late Paleozoic volcanoes. At the Taldybulak Levoberezhny Au deposit, the principal ore-controlling structures are inter- and intraformational shear, thrust-fault zones and tectonic mélange injected by intrusions that underwent metasomatic alteration. Gold-sulphide disseminated mineralization is associated with the upper part of Taldybulak shear zone and is associated with monzodiorites and quartz-tourmaline veinlets.
The Aktiuz ore field is located in an uplifted block of the basement rocks, including gneisses and crystalline schists (the Archean Aktiuz complex and Paleoproterozoic Kemin group). They are intruded by Late Ordovician-Silurian collision granites and granodiorites, Devonian monzodiorites, alaskites, alkalic and subalkalic two-feldspar granites, and Permian-Triassic syenites, subalkalic leucogranites, granophyres.
The Kuperlisay leucogranite intrusion is an elongated body with several ridge-like projections of granophyres. The Aktiuz ore field contains deposits of thorium at Kuperlisay; of REE, Nb, Ta and base metals - at Kutessay and Aktiuz; of beryllium - at Kalesay. All are hosted by leucocratic alkali granites, granophyres, granite-porphyries and albitites.
Key words: Geodynamics, gold, REE, rare-metals, genetic model.