The arcuate – structures on space borne remotely sensed imagery : their genesis and domination in gold mineralization
Lin Qizhong, Guo Huadong, Shao Yun
Institute of Remote Sensing Applications, Chinese Academy of Sciences,
P.O. Box 775, Beijing 100101, P.R.China
Abstract
It is discovered that the arcuate image anomalies are well-developed in Xinjiang, northwestern China with the interpretation of spaceborne remotely sensed images. They have’ regular dimention, orientation and distribution. The conclusion of the study is : they are specific geological bodies formed under special conditions during the geological evolution course. They study area is located at the connection of Siberia plate and Junggar plate, where is sedimentary formation of volcanic and pyroclastic rocks. A series of grand abyssal faults, developed in early stage and strike in NWW direction, are the major dominating structures during the tectonic evolution in the study area. Owing to the strike slip and shear movement, stress concentrates in some sections of the faults, where rocks are fractured and low-medien hydrothermal alteration are well developed. The non-uniform of physical property of rocks and stress distribution took shape the arcuate structures in various of genetic mechanism. The arcuate structures have typical brittle shear zone character. Their evolution synchronized low –medien hydrothermal alteration. If they developed in “Mineral source” strata, they would be favourable for gold and copper enrichment and macro indicators for mineral exploration in use of Remote Sensing. This paper presents the image characteristics of arcuate structures and their emergence and developing, discuss their genesis and dominating in mineralization.
Introduction
The most important contribution of spaceborne Remote Sensing to geology is its ability to show the pattern and distribution of structures and indirectly express the mineralization process. The Landsat MSS, TM, SPOT HRV image how a number of arcuate imagery features (numbered as 1 1 – 5 in fig. 1) within Ertix structural zone in northwester China. They are assemblage of geological
bodies in arcuate shape including structures, metamorphic rocks and a few relic blocks with typical tectonic characters and consistent evolution process. More-over they are strongly related to the formation of low-medien hydrothermal mineral deposits. They its why they are named as acrcuate structures. This paper discuss their genesis and domination in mineralization.
Figure 1. Distribution Map of Arcuate Structures in Ertix Region
The Characteristcs of Arcuate Structures
1) Obvious image tone anomalies in arcuate shape
The tone anomalies are the most distinctive and recognizable character of arcuate structure. Each of arcuate structure is in sharp contrast to the image background:
- dark tone anomalies against the background in light tone such as No. 1 arcuate structure in fig. 1.
- An image anomalies in dark tone come out of light background such as No. 5.
2) Regular extension and distribution
It is easily delineate the arcuate structures on the space borne image. They extend tens kilometers long and number kilometers, even more than ten kilometers wide, and occupy hundred square kilometers area. The No. 3 arcuate structures, one of them, extends eastwards into Mongolia. The arcuate structures mainly protrude to south which means the compressive stress comes from north.
3) Similar lithological combination in Hercynian formation.
All of late Palaeozoic strata expose in Ertix region. The arcuate structure
are strongly related to the middle Devonian and early Carboniferous rocks which are volcanic formation consists of felsic or femic volcanic rocks, pyroclastic rocks, clastic rocks interbeded with carbonatite.
4) Related to composite folds
The arcuate structures developed ins strongly folded strata, especially in linear tight composite synclines.
5) Develop along large abyssal faults and controlled by large compressive and torsional faults.
The arcuate structure developed at lateral part of large abyssal faults and strike in parallel with them (fig. 1). These faults play an important domination role in tectonic evolution of Ertix region. They are typical compress ional faults or torsional faults with compressive fracture zone in tens or hundreds meters wide. Schistosity, mylonitization, breccia and compressive lends are well developed within the fracture zone. In some section of the faults are the Devonian rock thrust over the Mesozoic rocks. Some of the arcuate structures are surrounded by faults, such as No. 1, no. 3 and No. 4, they have faults boundaries, which make the arcuate structures be a relatively independent “micro tectonic units”.
