GISdevelopment.net ---> AARS ---> ACRS 1990 ---> Geology Disaster

Multi-Source remotely sensed data applied to gold and nonferrous metals exploration in Xinjiang region

Guo Huadong,Lin Shudao,Gui Chengyu,Lin Qizhong
Zhang Shengkai,Zhu Chongguang,Li Naihuang
Institute of Remote sensing Application , Academia Sinica
Beijing, China


Abstract
An experiment of remote sensing for mineral exploration has been carried out in Northern Xinjiang Region in the use of Landsat TM MSS, SPOT HRV, NOAA AVHRR, National Land Resource Survey Satellite data, airborne synthetic aperture radar and colored infrared data. Considering the disparity of landscape and geological conditions of mineralization in each subarea of the study region, relevant study techniques and their combinations were chosen and various methods were developed for recognizing and identifying the mineralization. On the basis of field reconnaissance, geochemical prospecting,- electrical sounding, and detrical extraction and geological engineering test were applied to gold anomalous areas which were selected as emphasized study targets, which established a relatively complete system of remote sensing for mineral exploration, i.e. spaceborne remotely sensed data for reconnaissance over large area- airborne data for locating position-geochemical and geophysical data for identifying the quality geological engineering test for determining the quantity. More than 10 gold, tin and copper deposit targets and prospective targets have been discovered and determined. Some amounts of scientific prospective reserve of gold mines have been evaluated from one of the gold targets.

Introduction
Xinjiang Region is located in the central part of Eurasia, most of it are arid, sparse vegetation cover, well rock exposure and a low degree geological work being done. Therefore, remote sensing technology has prominent advantage to working in this area. In the last three years, remote sensing for mineral exploration in the Northern Xinjiang have been undertaking. The chief aim is to exploite gold and nonferrous metal resources,'

The study area of this program covers more than 100,000 square kilometers including Altaimountain and Junggar depression. Its tectonic position lies within Altai and Junggar folding zone with Paleozoic meta-volcanic and meta-sedimentary rocks and well-developed basic-acidic intrusions. It is obvious that over such a large area everything is disparity: different landscape, complicated structures which control mineralization, various mineralized rorks and metalogenetic conditions, which lead many different ore deposits existing in the study area. In order.

To find out the mineral deposits, the key step is to work out the most efficient and effective techniques for mineral exploration using remote sensing.

Recently a great number of number of romote sensing geologists are seeking the techniques and methodology of remote sensing for mineral exploration. In consideration of factors mentioned above and aims of the program which is to explore as much gold and nonferrous metals resources as possible, the principle of program is determined to use multi-source remotely sensed data as major techniques and supported by geochemical and geophysical work. It is necessary for the program's aim to develop relevant techniques and methods and their combinations according to characteristics of targets.

Techniques and Methodology
The eight types of remotely sensed data have been collected in the Northen Xinjiang including 5 types spaceborne data, Landsat TM, MSS, SPOT, NOAA AVHRR and MSS are efficient at searching and determining the emphasized study areas. TM is capable of identifying the alteration zone due to its high spectral resolution. Because of their high special resolution, SPOT HRV and colored infrared data become the major information sources for analysing the geometric feature of mineralized geological bodies. Radar data has prominent advantages in structure interpretation. As a kind of complement data, National landsat data play an important role, especially in area without other data cover.

In this study, platform includes both space borne and airborne, wavelength covers visible, infrared and microwave, the emphasized study areas were covered by all three kinds of wavelength. The image resolution varies from 2m to 100m which suits different demands of study. This is one of the key techniques of the program and is effective an economic. The second key technique is information extraction: start from understanding the imaging mechanism of mineralized geological body, analyse the anomalous image features, develop effective methods, extract mineralization information. The third one is to integrate remotely sensed data with geological geophysical and geochemical data. Through the comparison and integration of multi-source data the best analysis results are reached.

Figure 1 demonstrated the procedures and techniques of the study. On the basis of it, a series of methods of remote sensing for mineral exploration were established.
  1. Gold-bearing Information Extraction. TM data with plentiful spectral information have capability of identifying mineralization and alteration. Using medium infrared bands and visible bands to do ratio and colour composite image processing on TM data in the Eastern Altai found out the ferritization and gold mineralization; Using KL transformation found out gold mineralized epidotization, which are important contributions of TM of discover fracture zone type of gold deposit in this area. Applying HIS transformation to SPOT data in the western Altai, which is to transform from Red, Green and Blue space to Intensity, Hue and Saturation space and their reverse transformation, extracted quartz veins from middle-acidic intrusions, A lot of veins are gold bearing quartz vein type of gold deposit in this area.

  2. Integration of Multi-Source Remotely Sensing Data and Integration of Remotely Sensed Data with other Surveying Data. Visible and infrared data of TM and SPOT HRV were integrated with SAR data in study of gold deposit SAR data shows variation of relief; TM data stress the spectral features; SPOT HRV has high special resolution. Integration of SAR TM and SPOT


    Fig.1 Procedures of RS Mineral Exporation in XinJiang

    Data enhanced the geological information of gold mineralization. Mean while, in order to interpret the deep fault associated with Kesa copper deposit remotely sensed data has been integrated with aeromagnetic data and gravity data; image interpretation map has been in targeted with thematic geological map.

  3. Remote Sensing and Mathematical Geology. It was two types of analysing methods one is to build up mathematical prospective model using remotely sensed data and other surveying data. Another one is to analyse the trend surface of lineament density, which were interpreted from remotely sensed data. In a specified circumstance, lineament density usually strongly relate to gold mineralization. The high Lineament density areas interpreted from trend surface highly correlated to gold mineralization.3

  4. Geological Data Sets Analysis Supported by GIS-as One of Means for Mineral Exploration. Central Altai was Chosen as a test area. It was very contributive to our broad understanding of gold targets that using remotely sensed, geological, geophysical and geochemical data to extract gold mineralization features, set up DTM and analyse data comprehensively. Which were supported by ARC/INFO and GIST geographic information system software, respectively.

  5. Special Pattern Analyses of Lineaments. NOAA AVHRR is able to reveal more geological feature of deep subsurface comparing to other remotely sensed data in the study area. It was inferred from special pattern analysis of lineament that the pattern is the inner characteristics of regional structures. The spacial pattern corresponds to sturcture zones of different geological events. Coincides with regional features of graivity field and relates to mineral deposits inherently. Therefore, it has leading function for mineral exploration study.
Discovery of gold deposit targets
A number of gold targets have been rapidly discovered by means of above mentioned methods and techniques, on basis of regional metallogeny and supported by large amounts of fieldwork. Two types of gold deposit found in Altai are described herein.
  1. Quartz Vein Type of Gold Deposit Target. This gold deposit target is located in the Western Altai. It is realized using space borne data for reconnaissance over large area that this region is has good geological condition for mineralization. A series of faults lie in between of two major faults, which strike in WE direction and WWW direction respectively. It was identified on the imagery that a number of dark colour, polygonal geological bodies scatter over a large, light colour circular body which is a acidic-middle-mafic intrusion complex found out from existing geological data. The contact part of different intrusions usually is favorable for mineralization. Then the SPOT and airborne infrared images were interpreted. They reveal some very small "light dots" in complex. The fieldwork shows that they are single quartz vein or a group of quartz veins. Some of quartz veins are gold-bearing quartz veing, some contain native gold which is visible on samples.

    The systematic sampling and chemical analysis show high gold contents, which lead the basic understanding of quartz vein type of gold deposit in the Western study area. Subsequently, large scale remotely sensed imagery was applied to the study area and more than 200 quartz veins were found, the longest is 200-800 meters, and 1-12 meters wide. A quarter of them are gold bearing quartz veins. The average tenor is 9 grams/per ton, the highest is more than 300 grams/per ton. The results state that there is a potential quartz vein type of gold deposit.
  2. Altered Fracture Zone Type of Gold Target. Gold deposit is strongly associated with structures. The compressional structure is one of the typical containing structures for mineralization. One compress ional structure zone over 70 km long in We direction was discover from imagery interpretation in the Eastern Altai. It has obviously faded. It is inferred from metallogeny that altered fracture zone type of gold deposit is probably exist in the compression structure zone. The random and systematic sampling results show that 37.97% of one hundred samples reach the scattering mineralized coefficient, 10.14% reach rich mineralized coefficient, 4.35% reach mineralized coefficient. The conclusion to it is a large gold-bearing structure zone.

    In order to sift out mineralized geological bodies for mining from the gold-bearing Structure zone.

    In order to sift out mineralized geological bodies for mining from the gold-bearing structure zone, TM, SPOT and SAR data were interpreted and integrated to extract alteration information. The five gold-bearing geological bodies were founded. The highest tenor is over tens ppm. The mineralized rocks are Upper Devonian meta-volcanic rocks with fine quartz weins. It is an altered fracture zone type of gold-deposit target. The subsequent geological work has discovered several deposits for mining.
Discovery of nonferrous metal targets
The mineralization conditions for nonferrous metals are different from gold, so the techniques for exploration are different as well. Image interpretation needs to set up on the basis of well understanding of its specified mineralization characteristics. In the study area, copper deposits are strongly associated with mafic and ultra intrusions and distribute in the vicinity of deep fractures; tin deposits highly relate to granites and appear near the boundaries of boundaries of batholiths.

Understanding of geological conditions of mineralization will help to use remote sensing technology to explore minerals.
  1. Tin Target

    A large biotite granite batholith-Kalamaili granite batholith-distributes in the eastern marging of Junggar depression. Spaceborne data, especially airborne data obviously reveal the special feature and spectral feature of the batholith which provides ideal image marks to mineral exploration using remote sensing techniques. Through setting up the interpretation standards for known deposits, guided by regional metallogeny of tin deposits in tin spar form exist in greisen veins within granite batholith. The vein groups can be directly interpreted from the large scale airborne photographs. The chemical analysis results show that 70% of samples are tin amomolous rocks. It is a promising tin deposit for mining.

  2. Copper Target

    A 50km long are form structure zone was interpreted from imagery in central Alitai. The integration of aeromagnetic data with imagery and field work has proven its existence. Moreover, it controls mineralization. The front of arc-form zone usually is favourable position for mineralization. The 18 small mafic intrusions have been found out firstly. On the basis of regional metallogeny these small intrusions are favourable for copper or nickel mineralization.

    Systematic filed work has been applied to these small intrusions. Special detailed work has been done on intrusions which lie in conjuction of arc-from structure and other large faults. The four of the of intrusions have good mineralization. The chemical analysis show that copper reach mining tenor and minerlization is getting richer from surface to deep surface. It is a meaningful copper target.
Checking by Geological Engineering
Over 10 gold, copper and tin deposits have been rapidly discovered by using multi-source remote sensing data. However, the ability of remote sensing techniques is confined to surface stage for mineral deposits assessment. Therefore, it is necessary to carry out geological engineering test on some of targets. Here take quartz vein type of gold deposit in the Western Altai as an example.

First of all is to apply large-scale geochemical test to mineralization zones that were interpreted from remotely sensed data. The geochemical anomaly distribution confirms the mineralization zones identified on imagery and determines the two dimensional range of gold deposits. In order to obtain the downward depth of quartz veins electrical sounding has been used.

Gold-bearing quartz veins exist in hornblende gabbros and plagioclase granites. In the study area. Almost all of the quartz veins have pyritization. Quartz veins with impregnation-distributed pyrites have different resistively and apparent polarizability from country rocks. There it is possible to measure the downward depth of gold-bearing quartz veins by means of electrical sounding. The measurement of quartz vein mumber Q15 shows that its depth is more than 60 meters. The drilling result has showed that there are several layers gold-bearing geologic badies at the 100 meters below the surface. The geological engineering test evaluated tens of tons of scientific prospective reserve of gold, which can be a gold deposit for mining.

The most important achievement of this study is that a number of mineral targets were dis-covered, furthermore, its most critical importance is: no matter whether it is quartz wein type of gold deposit or altered fracture zone type of gold deposit no matter it is a copper deposit cotrolled by mafic complex or tin deposit controlled by greisenzation in granites, they all have their own specified image features and image anomaly. Consequently, under the some geological condition and landscape, the multi-source remotely sensed data and remote sensing techniques can rapidly discover more mineralization information.

Conclusion
More than ten gold and nonferrous metals resource for mining and further research have been rapidly discovered by using multi-platform and multi-band remote sensing technology. According to regional metallogeny, geological conditions and landscape features to develop effective combinations of techniques and methods is the key part of mineral exploration using remote sensing. In this study, a key of practical methodology of remote sensing for multi-source remotely sensed data to identify the position and characteristics, geophysical and geochemical work to determine the quality and quantify, finally, geological engineering test to measure the mineralization state. The study results clearly show that multi-source remote sensing technology is a rapid, economic and effective mineral exploration means, especially in the Northern China where there is low population over large area, sparse vegetation cover, and well rock exposure, and a low degree geological work done before.

References
  1. F. Jaskolla and J. Herkl, "Evaluation and Digital processing of Multispectral Spot Data", International Jonmal of Remote Sensing, Vol . 9. No 10-11, pp 1609-1630, 1998

  2. T. L. Purdy et al, "Use of Thematic mapper Data for Alteration and Geologic mapping in South-Central Nevada", The proceedings of the Fourth Conference Remote Sensing for Exploration Geology", 1985

Photo LANDSAT TM False Colour Composite Image in Eastern Altai.
The Bright Bands in Center are apart of Gold-bearing Aleration Zone