The Study On The Genesis And Characteristic Of Huachangyu Garnet

The garnet deposit situated at Huachangyu, Funing, Qinhuangdao was investigated. Samples of the garnet and its wall rocks were collected. The specimens were studied by lithofacies analysis (LFA), X-ray diffraction analysis (XRD) and X-ray fluorescence (XRF). The gemological characteristic parameters of the garnets were measured. The geological environment and its forming process were analyzed. The reservation of the garnet was estimated. The quality and economic value of the garnet were evaluated.The mineral composition of the garnet and its wall rocks were studied using LFA , XRD and XRF. The subspecies of the garnets were determined by XRD. Huachangyu garnet occurred in the skarn is mainly constituted of goldmanite. The skarn is situated on the contact belt between the granite and limestone. The Huachangyu garnet's formular is (Ca_3.2349Mg_0.0556Mn_0.0197)_3.2602 (Fe_1.8437Al_0.1733Ti_0.0045)_2.0215 (Si_2.8272O₁₂). The skarn is constitutive of hematite, chlorite, calcite, quartz, garnet and so on. Granite is constitutive of quartz, orthoclase, plagioclase, biotite, etc. The main component of limestone is calcite, which were marmorized obviously.For Huachangyu garnet, the main color are dark green and yellowish brown; the luster is strong vitreous; the transparency is opacity; the refractive index is 1.852; the density is 3.78 g/cm3; the Mohs hardness is 6⁷. The absorptive spectrum of the garnet is not characteristic. The ultraviolet fluorescence of the garnet cannot be seen. The color of the garnet is not change under the sun and under the incandescent lamp. It does not redden behind the Charles color filter. The granularity is between 1mm and 20mm. The samples of the garnet cannot be used as gem still.The forming process of the garnet was analyzed. Garnet is a kind of skarn mineral formed under the effect of contact metasomatism. It is deposited in the contacted belt between granite and dolomitic limestone. The granite was formedin Mesozoic Yanshan Period, about 200 million years ago. The limestone was formed in the Paleozoic era, about 500 million years ago.The garnet was formed in temperatures between 450℃, and 600℃, in pressure between 450×105 Pa and 108Pa. The garnet was formed in the depth of 1.6 km³.6 km. According to field survey, the dimension of the skarn belt is estimated. Its width is about 25m, depth 150 m and about 350 m in length. The reserves of garnet are about 4.9×105 t. The garnet which cannot be used as gems can be used for abradant and filtration.