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Geology/Disaster 2 |
Deposit Image Model and optimization of Prospect Targets
2. Research on Distribution Regularities of Gold Mineralization
Study on mineralization distribution regularities is the key link for establishing deposit image model and the basis for determining prognosis guides. Having done geological investigation in the field, we summarized the distribution regularities of gold mineralization in study area as follows:
- Gold mineralization distribution is obviously controlled by structures according to the image (scale 1:200000) interpretation, the strutural framework in study area consists of Palaeozoic central uplift zone and subsidence zones on the both sides of the uplift. Mineralized zones are controlled by deepseated faults which have undergone long-term activites, displaying distribution pattern of EM trending. The deposits are located at the intersections of NE and EW stricking faults and occur in high order and small scale fault strutures. Ore-body localizing strutures dominantly depend on mineralization type. Generally speaking, quartz vein type occurs in tensile structures, while altered rock type is located in compressive or compressive-shear structures.
- Gold deposits of Different type displays zonal distribution zonal distribution is obvious in Beishen region. On the whole , it can be partitioned in to three mineralized zone: i.e. north zone-volcanic-type gold deposit zone; middle zone-granite-type zone; and south zone-mixing type zoen. The south zone can be further divided into three subzones , i.e. north subzone granite-type zone, middle subzone-valcanic-type zone, and south subzone –metamosphic rock-type zone.
- Gold mineralization is restricted within gold-source formation
Intermediate- basic volcanic formation are important gold-source formation in the study area. For example , gold mineralization are strictly controlled by bimodal colcanic formation of lower proterzoic (the upper group) and intermediate-basic volacnic formation of Ordovician-Silurian system and carboniferous system, demonstrating that gold mineralization tends to be developed in pre-existing gold-source formation
- Gold mineralization is related to Middle-Late Variscian magmatism and hydro-thermalism
The grantie relevant to gold mineralization mostly are intermediate, intermediate acidic granite, belonging to a group of granodiorite and taking the shape of small irrefular instrusions, sush as offshoot, stock. gold mineralization has close time and space relation to hyrdrothermal activities derived from Variscian intermediate acidic magmatism whic provided favourableconditions for gold migration and concentration.
3. Establishment of Deposit Image Model
Deposit image model means comprehensive expression of typical image features of Major orecontrolling factors including strutures, formations, dikes, and so on. Since the genesis of gold deposits is quite complicated and recognition of deposit image signatures involves a wide range of methods and technologies. The deposit image model in question is established on spectral charcteristics of surface objects. Based on image processing, geological interpretation, study on gold mineralization distribution regularities and field ckeck, image features of various orecontrolling factors and recognition criteria have been extracted. Different-type deposit image models in study area have been summarized as follows:
A. Granite-type gold deposit image model
- Gold- productive intrusive bodies are Variscian granite , granodiorite in the shape of stock and offshoot. Granite in the region has higher reflectance,showing grey,light-grey colour by which it is easily discerned in the image. Granite bodies are controlled by east-west orientation faults, and distributed in zonal and branch-like forms and inthe shape of bead string.
- Dikes and alternations are well developed in gold-productive granite bodies, demonnstrating uneven grey and mottled colour in the image, such as Jinbguozi and shijinpo granite bodies.
- deposit is controlled by regional east-west striking, occuring in its subsidary faults. for example, Jinguozi deposit is controlled by a group of subsidary NNW striking quartz veins, exhibiting distinct light orange linear feature in the image.
- there is “colour anomaly” in the range of every deposit. Different manifestations of image signatures are obtained by using diferent image methods. For example, “colour anomaly” of Mojindong area displays light purple colour which differ from that of surrounding granite in the colour composite image (4,5,7 bands) . While in the ratio composite image (5/7, 5/4, 5/1), Jinguozi diposit is expressed as bright light orange colour. The same “Colour anomaly” can be seen at No. 210 blind deposit which is located in the south of Jinguozi deposit (fig.2) . These colour must be caused by widespread altered rocks closely associated with gold mineralization in the range of deposit.
Figure 2 Ratio composite image
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