SUMMARY

Geological characteristics and coal resources in the mainland of Sông Hồng basin

according to new research results

Đồng Văn Giáp, Phí Chí Thiện, Lê Duy Nguyên, Đinh Đức Anh, Nguyên Văn Thu

The research results of the project “Overall investigation and evaluation of coal resources in the mainland of Song Hong basin” is confirmed that the study area has formation in order from bottom up as follow: Phù Tiên (E₂pt), Đình Cao (E₃đc), Phong Châu (N₁¹pch), Phù Cừ (N²₁pc), Tiên Hưng (N³₁th), Vĩnh Bảo (N₂nv), Hải Dương (Q₁hd), Kiến Xương (Q₂kx). In which, the Tiên Hưng coal-bearing formation has been divided in detailed into five stratigraphy sub-formations containing five coal sub-seam and identified three main structural zones which are Khoái Châu - Tiền Hải uplift block, Quỳnh Phụ - Thái Thụy subsidence block, Xuân Trường structural block (Vũ Tiên); three petrotectonic assemblages, including: Pre - Cenozoic basement, Eocene - Miocene, Pliocene - Quaternary. The Northwest - Southeast slip fault systems have been determined the location, scale and properties according to 2D seismic data including strike-slip faults of Sông Chảy, Thái Bình, Vĩnh Ninh, Sông Lô, Kiến Xương, Tiền Hải. The Northeast - Southwest slip fault systems have the role in dividing the blocks, forming the onyx uplift - subsidence structure and, tending to sink deeper towards the sea. The large folds consist of the Quỳnh Phụ - Thái Thụy synclinorium; the Phù Cừ, Đông Hưng, Kiến Xương - Tiền Hải, Vũ Tiên synclines; the Tiền Hải, Kiến Xương anticlines. The hydrogeological and engineering geology characteristics of the coal bearing and upper strata were preliminarily evaluated. The water bearing capacity of the Tiên Hưng coal-bearing formation is relatively high. In chemical composititon, the groundwater is of sodium chloride, the total dissolved solids content is 13,48 g/l. The rock cohesion is very weak to moderate and the average compressive strength as follows: claystone - 120,45 kG/cm2; roof and floor rocks of coal seam: sandstone - 4,28 kG/cm2, siltstone - 20,4 kG/cm2, claystone - 110,65 kG/cm2, Coal - 15,54 kG/cm2.

The five coal seam members (TV) distributing in five members of the Tiên Hưng formation have been identified, including: five coal seams of TV.1, 23 main seams and 12 sub-seams of TV.2, 18 main seams and seven sub-seams of TV.3, 10 main seams and two sub-seams of TV.4, three seams of TV.5. The total coal resources (333 + 334a + 334b class) are 212.676.990 thousand tons, of which 334a class be 24,396,726 thousand tons; 333 class be 5.649.218 thousand tons, including: Bình Minh - Khoái Châu area - 845,696 thousand tons and the new estimation area covering 265km2 (Đông Hưng - Tiền Hải, Thái Bình province and Giao Thủy, Nam Định province) - 4,803,521 thousand tons. The coal is at a good quality, belonging to the lignite A to bituminous coal rank, with the average values: Wpt - 17,40%, AK - 10,34%, V°h - 47,65%, Qk - 6.191,15 Kcal/kg, Qch - 6.899,12 Kcal/kg, Skch - 1,14%, Pk - 0,008%, d - 1,34g/cm3.

Keywords: Tiên Hưng, coal seam, coal sub-seam, Sông Hồng, Resources