The chemical composition of basic-ultrabasic rocks in Panxi area is different because of its ore-bearing property and location. The analysis data of some rock masses and Emeishan basalt submitted for inspection are listed in Table 4-3 ~ Table 4-8.
The chemical composition of Dayanzi ultrabasic rocks (mainly olivine pyroxenite) has little change, with SiO 235.62% ~ 42.58%, TiO 20.93% ~ 1.3%, Al2O35.26%~8.5% ~ 8.5%, Feot12.48%. Carbonization makes the content of CaO change greatly (3.9% ~ 10.8%), the content of K2O+Na2O is low (0.2 1% ~ 0.5 1%), P2O50. 12% ~ 0.2%, H2. The rock is strongly altered, m/f 2.04 ~ 3. 16, belonging to iron ultrabasic rock (Table 4-3). SI (consolidation index) is 50.62 ~ 6 1. 19, which indicates that Dayanzi ultrabasic rock belongs to the product of early magmatic evolution.
Table 4-3 Composition Table of Macroelements and Trace Elements of Ultrabasic Rock in Dayanzi Mining Area, Huili, Sichuan Province
sequential
Note: The sample 1 was analyzed by Southwest Institute of Metallurgical Geology and Chengdu University of Technology; The main elements of samples 2 ~ 7 were analyzed by Yichang Institute of Geology and Mineral Resources of the Ministry of Land and Resources, and the trace elements were detected by Institute of Geophysical Exploration of the Ministry of Land and Resources. The unit of contents of major elements is 10-2 and trace elements are 10-6, among which platinum, palladium, gold and silver are 10-9.
Table 4-4 Table of Major Elements and Trace Elements of Ultrabasic Rock and Mineralized Dolomite in Dayanzi Mining Area, Huili, Sichuan Province
sequential
Note: Tested by Yichang Institute of Geology (major elements) of Ministry of Land and Resources and Institute of Geophysical and Geochemical Exploration of Ministry of Land and Resources. The contents of major elements are 10-2, platinum, palladium, gold and silver are 10-9, and copper and nickel are 10-6.
Table 4-5 Composition Table of Major Elements and Trace Elements of Emei Mountain Basalt and Its Dark Rock Series in Longzhaoshan Area
Note: According to the analysis of Yichang Institute of Geology and Institute of Geophysical and Geochemical Exploration of the Ministry of Land and Resources, the contents of major elements are 10-2 and trace elements are 10-6, among which platinum, palladium, gold and silver are 10-9.
Table 4-6 Composition Table of Major Elements, Trace Elements and Metallogenic Elements of Xinjie ZK30 1 Bored Rock Mass and Emei Mountain Basalt
Note: The samples were analyzed by Southwest Institute of Metallurgical Geology and Chengdu University of Technology (neutron activation). The main element is 10-2 and the trace element is 10-6, in which platinum, palladium and gold are 10-9.
Table 4-7 Contents of Macroelements, Trace Elements and Platinum Group Elements in Rock Mass and Basalt of Xinjie ZK10/and ZK 104.
Note: Macroelements are determined by Guangzhou Institute of Geochemistry, China Academy of Sciences, platinum group elements are determined by Joint Open Laboratory of Nuclear Analysis, China Academy of Sciences (Li Analysis), and other elements are analyzed and tested by Chengdu University of Technology. The content unit of major elements is 10-2, platinum group elements and Au are 10-9, and other elements are 10-6.
Table 4-8 Contents of Macroelements, Trace Elements and Platinum Group Elements in the borehole samples of ZK 104 and ZK 18 1 Xinjie Rock Mass
Note: Macroelements are determined by Guangzhou Institute of Geochemistry, China Academy of Sciences, platinum group elements are determined by Joint Open Laboratory of Nuclear Analysis, China Academy of Sciences (Li Analysis), and other elements are analyzed and tested by Chengdu University of Technology. The content unit of major elements is 10-2, platinum group elements and Au are 10-9, and other elements are 10-6.
Gabbro and diabase occur at the edge or top of Dayanzi ultrabasic rock body, and their chemical compositions are SiO 243.62% ~ 52.48%, TiO 2 1.09% ~ 1.99%, Al 2O 310.28% ~1. MgO is 6.86% ~ 1 1.07%, CaO changes greatly due to carbonization (0.63% ~ 10.4%), K2O+Na2O content is low (0.42% ~ 2.33%), and P2O50.24% ~. The degree of rock alteration is obviously different, m/f1.30 ~1.81,which belongs to iron-based rocks (Table 4-3). SI (consolidation index) is 38. 19 ~ 48.45, which reflects a petrochemical feature close to the original magma composition (most of the original basaltic magma has a SI of about 40 or higher).
The square Shi Ying in Qingshuihe rock mass contains 238.58% ~ 44. 12% SiO, 2 1.03% TiO, 35. 15% Al 2O and Feot1.64%. MgO is 24.2% ~ 24.8%, K2O+Na2O is relatively high (0.9 1% ~ 1.29%), P2O50.11%~ 0.3%. M/F 2.63 ~ 4.04, belonging to iron ultrabasic rocks (Table 4-5); SI is 57.3 1 ~ 66.52, which belongs to the product of crystallization in the early stage of magmatic evolution.
Gabbro or diabase in Qingshuihe rock mass contains SiO 249. 1% ~ 55.4%, TiO 2 1.56% ~ 1.96%, Al2O3 9.48% ~ 14.28%, Feot/kloc-. p2o 50.3% ~ 0.4%； M/f1.17 ~1.86, belonging to iron basic rocks (Table 4-5); Si 32.95 ~ 4 1.89, close to the original basaltic magma composition.
Emeishan basalt and fine-grained gabbro (vein) on Longjiao Mountain belong to iron-basic rocks (m/f 0.63 ~ 1.33), and their chemical compositions are very similar (Table 4-5). The content of SiO2 _ 2 in fine gabbro is relatively low (4. 1% ~ 4.7%) and. The consolidation index (SI) of rocks is between 265,438+0.8 ~ 35.4, indicating that magma has undergone obvious crystallization differentiation.
The floor of Xinjie rock mass is basalt. Due to the influence of plagioclase content in basalt and rock alteration degree, its chemical composition changes greatly (XJ6 in Table 4-6 and X 10 1-32 in Table 4-7), SiO2 3 1.47% ~ 40.24%, TiO 24.38% ~. al2o 3 12.5 1% ~ 14.27%，FeOT 16.26%~ 19.79%，MgO 6.52%~6.59%，K2O+Na2O 2.22%~2.96%，p2o 50.06% ~ 0.53%； M/f 0.50 ~ 0.7 1, belonging to iron-rich and titanium-rich basalt. The top basalt of Xinjie rock mass (XJ-34-2 in Table 4-6) contains relatively high amounts of SiO2, TiO2 1.94%, Al2O3 13.48%, FeOT 10.85% and MgO 5.02%. M/f 0.8 1 belongs to the basalt which is poor in titanium, rich in alkali and rich in silicon.
Judging from the chemical composition of basalt, floor basalt is generally equivalent to picrite basalt, while roof basalt belongs to basaltic andesite, which tends to transition to basaltic trachyandesite.
There are many rock types in Xinjie rock mass, including peridotite, pyroxenite and gabbro, and the content of SiO2 _ 2 in the rock mass varies greatly (38. 1 1% ~ 50.97%). TiO _ 2 is 20.96% ~ 6.7 1%, and more than 5% of TiO _ 2 content is related to gabbro. Al2O3 2. 17% ~ 20.08%, the content is related to plagioclase content; Feot10.56% ~ 21.31%,the high iron content is mainly related to peridotite and pyroxenite facies; MgO 2.5 1% ~ 26.03%, the low content is related to gabbro; CaO is 4.84% ~16.11%,which is mainly enriched in plagioclase and clinopyroxene, making the Cao content in pyroxene-bearing rocks greater than 13.7%. The content of K2O+Na2O varies greatly from 0. 17% to 5.29% (average 1.3 1%), and the high content is related to gabbro. P2O50.02%~0.65%。 The male/female ratio varies greatly. For gabbro or gabbro-gabbro, m/f varies from 0.3 1 to 1.62 (average 1.04). For peridotite, pyroxenite and rocks containing pyroxenite, the m/f is 1.67 ~ 2.54 (average 2.17); Xinjie rock mass is mainly composed of iron ultrabasic rocks and iron basic rocks, and a few samples are iron-rich ultrabasic rocks and iron-rich basic rocks. About 90% of the samples in rock mass have the characteristics that Na2O content is greater than K2O.
In addition, the m/f value of Hongge rock mass ranges from 0.26 to 2.19 (average 1. 14), and most of them are iron-rich ultrabasic rocks and iron-rich basic rocks, and some of them are iron ultrabasic rocks and iron bedrock (Hu Sufang, 200 1.
Basic-ultrabasic rocks in Panxi area, in the silica-alkali diagram, except for a few samples of Xinjie, Hongge, Limahe and Qingkuangshan, are classified as alkaline series area, and all the other samples are classified as subalkaline series area (Figure 4- 13a).
Fig. 4- 13 Silica-Alkaline Map of Basic-ultrabasic Rocks in Panxi Area
(The base map is based on T.N. Owen, 197 1)
S- subalkaline series; A- alkaline series; α-basic-ultrabasic rocks in Panxi area: b- Emeishan basalt; After deducting H2O and CO2 from the sample, it was converted into 100%, and some data were published by ourselves.
Fig. 4- 14 AFM diagram of subalkaline magmatic rocks in Panxi area
(The base map is based on T.N. Owen, 197 1)
T-type tholeiite series; Carbon-calcium alkaline series
Most of Emei basalts in Emei Mountain, Longzhao Mountain, Xinjie, Ertan and Yangliuping in Emei igneous province are classified as subalkaline series (Figure 4- 13b). It can be seen from Figure 4- 13 that the alkali (K2O+Na2O) content of Emeishan basalt is often slightly higher than that of basic intrusive rocks in the same period.
The subalkaline rock samples (Figure 4- 13) are put into Panxi area, and after further projection on AFM diagram, it is found that the components of Dacao, Dayanzi, Qingshuihe, Qingkuangshan, Lima River, Walnut Tree, Yanghewu, Hongge and Xinjie rock bodies in Panxi area are all put into tholeiite area, among which, due to the high iron content of Hongge and Xinjie rock bodies, Longjiao Mountain and Xinjie rock bodies are all put into tholeiite area.
Basic-ultrabasic magma in Panxi area can be roughly divided into two types: low iron and high iron. Most samples belong to low-iron type, and with the increase of FeOT content, the content of TiO2 in rocks tends to decrease (Figure 4- 15). Most samples in Xinjie rock mass and Hongge rock mass have high FeOT content (> 16%), and only a few samples have relatively low iron content, which generally belong to high iron type, and at the same time reflect that the magmatic differentiation of layered rock mass is very developed. In addition, the FeOT content of Emeishan basalt is relatively low, and some samples of Xinjie and Hongge rock bodies also have high TiO2 content (Figure 4- 15).
There is an obvious negative correlation between Al2O3 and MgO content of basic-ultrabasic magma in Panxi area (Figure 4- 16), and the MgO content of Emeishan basalt is usually low and Al2O3 content is relatively high. The Al2O3 content in most samples of Xinjie rock mass and Hongge rock mass is relatively low (Figure 4- 16).
Fig. 4- 15 diagram of FeOT-TiO2 _ 2 relationship of magmatic rocks in Panxi area
Fig. 4- 16 Relationship diagram of Al2O3-MgO of magmatic rocks in Panxi area
The content of TiO2 _ 2 in basic-ultrabasic magma in Panxi area is negatively correlated with m/f ratio (Figure 4- 17). Most ultrabasic rocks belong to iron (m/f ratio is 2-6), a few are rich in iron (part of red lattice rocks), and some samples are magnesium ultrabasic rocks (big trough rocks). Most samples of basic rocks belong to iron basic rocks (m/f value is 0.5 ~ 2), and the m/f ratio of Emeishan basalt is mainly between 0.5 ~ 2. Through careful comparison, it can be found that the m/f ratio of Emeishan basalt in Panxi area is mostly around 1, while the m/f ratio of most basic rocks is slightly higher than that of basalt (mostly around 1.5), and generally has a low TiO2 content (Figure 4- 17).
As for the relationship between TiO _ 2 and P2O5 in Emeishan basalt, as can be seen from Figure 4- 18, there is a positive correlation between them. The contents of TiO _ 2 and P2O5 in the basalt in Yangliuping area are relatively low, while the contents of TiO _ 2 and P2O5 in the basalt in Emei Mountain in Longjiao Mountain, Ertan and Emei Mountain are generally high. In Xinjie area, the enrichment of vanadium-titanium magnetite in layered rock mass leads to a relatively low content of TiO2 in basalt.
Fig. 4- 17 relationship diagram of TiO _ 2-m/f of magmatic rocks in Panxi area
Fig. 4- 18 P2O5-TiO2 _ 2 Relationship Diagram of Emei Mountain Basalt
Layered rocks such as Xinjie and Hongge show a wide range of TiO2 content and P2O5 content. Generally, the content of TiO2 is more than 3% or the content of P2O5 is more than 0.5% (Figure 4- 19). The contents of TiO2 _ 2 and P _ P2O5 _ 5 in basic-ultrabasic rocks in other areas are relatively low, and there is a certain positive correlation.
Fig. 4- 19 P2O5-TiO2 _ 2 relationship diagram of basic-ultrabasic rock mass in Panxi area
Second, the characteristics of trace elements
The composition characteristics of rare earth elements and trace elements of basic-ultrabasic rocks in Panxi area are obviously different due to different magma sources and evolution processes (Table 4-3 ~ Table 4-8).
On the Tb/Yb-Ti/Y diagram (Figure 4-20), most samples of Emeishan basalt in Longjiao Mountain, Ertan and Xinjie areas in Panxi area are projected in a relatively concentrated area (Figure 4-20 Emeishan basalt area), showing a relatively high ratio of Ti/Y and Tb/Yb.
The Ti/Y ratio and Tb/Yb ratio of most samples of Hongge rock mass are much higher than those of Emeishan basalt, and some samples are cast near Emeishan basalt area. The composition point of Xinjie rock mass is mainly located in Emei Mountain basalt area and its vicinity. The basalt sample of 1 Xinjie floor shows the geochemical characteristics of Hongge rock mass (Figure 4-20). Basic-ultrabasic rocks in other areas have relatively low Tb/Yb ratio or Ti/Y ratio.
The distribution curves of rare earth elements in basic-ultrabasic magma in different areas have their own characteristics:
(1) Basic-ultrabasic rocks containing copper, nickel and platinum in Dayanzi, Juglans regia, Qingshuihe and Qingkuangshan. The distribution curve of rare earth elements belongs to the smooth right-leaning type (Figure 4-2 1b, 22f, 22h), and its (La/Sm)N is 2.56 ~ 3.57 (the average value of 20 samples is 2.7), which is a light rare earth enrichment type. Rare earth elements are highly fractionated, and (La/Yb)N is 5.85 ~ 19.82 (average 9.9). The fractionation of heavy rare earth elements is strong, and (Tb/Yb)N is 1.63 ~ 3.0 (average 2. 19). Europium is basically normal, and its δEu is 0.84 ~ 1.09, with an average value of 0.97.
(2) The basic-ultrabasic rocks of Lima River contain copper-nickel sulfide. The distribution curve of rare earth elements belongs to a smooth right-leaning type (Figure 4-2 1c), and its (La/Sm)N varies from 2.33 to 2.84 (the average value of 6 samples is 2.5). Rare earth elements are highly fractionated, and (La/Yb)N is between 8. 18 ~ 15.09 (average 10.70). Heavy rare earth elements are strongly fractionated, with (Tb/Yb)N of rocks being 1.98 ~ 2.95 (average 2.47) and δ EU being 0.89 ~ 0.98, average 0.95. Generally speaking, it is similar to the REE abundance of Dayanzi and Qingshuihe rocks in Huili.
Figure 4-20 Relationship Diagram of Tb/Yb-Ti/Y of Basic-Ultrabasic Rock Body in Panxi Area
(3) Layered rock bodies containing PGE in Panzhihua, Hongge and Xinjie.
Panzhihua Rock Mass: The distribution curve of rare earth elements shows that medium rare earth elements are highly enriched (Figure 4-2 1f), and the abundance of light rare earth elements is obviously greater than that of heavy rare earth elements, and its (La/Yb)N is 3.19 ~ 5.45; It is characterized by weak fractionation of light rare earth elements, (La/Sm)N is about 1, while heavy rare earth elements are obviously fractionated, (Tb/Yb)N is 2.24 ~ 3.11; The abnormal characteristics of europium in rocks are obvious, and δEu is 1.24 ~ 1.46.
Hongge rock mass: The REE abundance of Hongge rock mass varies greatly (Figure 4-2 1d), and the partition curve can be divided into three situations: ① Light REE is relatively rich, but the REE abundance value is low, and there is almost no obvious fractionation of light REE, and its (La/Sm)N is 0.51~1. This is the main body of Hongge rock mass, which is related to the low alkali content in the rock mass, and its K2O+Na2O content is less than 1%. (2) Light rare earth elements are remarkably enriched and highly fractionated, with (La/Sm)N of 5.2 ~ 6.9 and (TB/Yb) n of 1.4 ~ 3. 1.5. The strong fractionation characteristics of light rare earth elements are related to gabbro or gabbro-bearing lithofacies. The content of silica in rocks is high (more than 42%), the content of titanium dioxide is low (2.2% ~ 2.4%), the content of alumina is more than 65438 0.4%, and the content of K2O+Na2O is high, which is 2.765438 0% ~ 4.56%. ③ The distribution pattern of heavy rare earth elements is intense fractionation, while the fractionation of light rare earth elements is not obvious. Its (La/Sm)N is 1.3 ~ 1.9, and its (Tb/Yb)N is 4.3 ~ 4.9. The characteristics of rare earth elements are related to low SiO2 _ 2 content (< 34%), relatively rich Al (Al(al2o 3 > 6%%), rich Ti (TiO _ 2 28.2% ~ 9.1%) and rich alkali (K2O+Na2O content 1% ~ 2.3%). The rocks are rich in P2O5, and the abundance of rare earth elements increases significantly.
Xinjie Rock Mass: The abundance of rare earth elements in the rock mass varies greatly (Figure 4-2 1g), but there is no obvious difference in the characteristics of rare earth elements in gabbro, pyroxenite and peridotite. The rocks are relatively rich in light rare earth elements, and the (La/Yb)N is 3.46 ~ 12.65 (25 samples average 7.83), while the degree of fractionation is low, and the (La/Sm)N is 1. 1 ~ 2.3 (average 1. The fractionation degree of heavy rare earth elements is moderate, and (Tb/Yb)N is 0.79 ~ 3.77 (average 2.28). The δEu value of rocks varies greatly (0.52 ~ 1.53), with an average value of 0.99. Generally, there is a weak negative europium anomaly at the top of pyroxenite (especially in PGE-bearing layer), but there is no europium anomaly or positive europium anomaly in peridotite and olivine gabbro.
Fig. 4-2 1 REE distribution model of basic-ultrabasic rocks and Emeishan basalt in Panxi area
(chondrite values are based on W.V. Boynton,1984; According to the data of Hongge rock mass, Hu Sufang, 2001; The rock mass data of Lima River, Walnut Tree, Qingkuangshan and Panzhihua are based on Yao Jiadong,1988; Ertan basalt data is based on Hong Zhong, 2006).
In addition, the (La/Sm)N ratio of fine gabbro (X 10 1-30) in contact with Emei basalt at the bottom of Xinjie rock mass is 2.9, the (Tb/Yb)N ratio is 1.76, and the δEu value is 1.5. Compared with its upper rock mass, it has the characteristics of positive europium with slightly higher fractionation degree of light rare earth elements and lower fractionation degree of heavy rare earth elements. This may be related to the fact that the rocks are rich in plagioclase and the Al2O3 content is as high as 20%.
(4) Emeishan basalt in Panxi area. The REE distribution curves of Emeishan basalt in Longjiao Mountain and Ertan areas are similar (Figure 4-2 1a, 22c), both of which belong to smooth right-leaning type, with the characteristics of relatively rich light REE, high REE fractionation and no europium anomaly.
The basaltic andesite at the top of Xinjie rock mass has obvious negative europium anomaly (δEu is 0.3 1), and the fractionation of light rare earth elements is obvious, but the fractionation of heavy rare earth elements is not obvious, with its (La/Sm)N ratio of 4.86 and its (Tb/Yb)N ratio of 1.43 (Figure 4-2/kloc-0
The europium anomaly of picrite basalt at the bottom of Xinjie rock mass is not obvious (δEu value is 0.76 ~ 1.06), the fractionation of light rare earth elements is low, and the fractionation of heavy rare earth elements is obvious, with (La/Sm)N ratio of 1.39 ~ 2.53 and (Tb/Yb)N ratio of 2.48 ~ 4.63.
Basic-ultrabasic rocks in Panxi area show obvious differences on the diagram of rare earth elements Tb/Yb-La/Sm (Figure 4-22). The distribution range of Longjiao Mountain basalt and Ertan basalt is relatively narrow, and there is a positive correlation between them. Xinjie basalt has a large distribution range.
The composition points of basic rocks and ultrabasic rocks of Dayanzi, Qingshuihe, Qingkuangshan, Walnut Tree and Limahe are basically distributed near the composition points of Longjushan basalt (Figure 4-22).
Figure 4-22 Tb/Yb-La/Sm relationship diagram of basic-ultrabasic magma in Panxi area
The composition points of Hongge rock mass and Xinjie rock mass are widely distributed, and the ratio of Tb/Yb and La/Sm is often high or low, which is significantly different from the above-mentioned rock mass, reflecting the significant difference in magma origin and evolution between them.
On the La/Sm-La diagram, the La/Sm ratios of most basalt samples from Longzhaoshan and Ertan areas and basic-ultrabasic rocks from Dayanzi, Qingshuihe, Qingkuangshan, Juglans regia and Lima River are close (Figure 4-23), which may imply that these rocks and Emeishan basalt are the products of crystallization differentiation of homologous magma. The composition points of Panzhihua rock mass, Hongge rock mass, Xinjie rock mass, some Xinjie basalts and Longzhaoshan basalt show an obvious positive correlation between La/Sm and La content (Figure 4-23), which may imply that the relationship between these rock masses and Emeishan basalt is mainly the product of magma crystallization with different melting degrees during the evolution of homologous magma.
Figure 4-23 La/Sm-La diagram of basic-ultrabasic magma in Panxi area
The abundance values of trace elements in basic-ultrabasic magma in Panxi area vary greatly (Table 4-3 ~ Table 4-8). Generally speaking, there are significant differences in trace elements cobwebs among Emei basalt, basic-ultrabasic rocks containing Cu, Ni and PGE, and well-differentiated layered basic-ultrabasic rocks (Figure 4-24).
Basalt is rich in low field strength elements th, Rb or Ba, while high field strength elements Y and Yb have low abundance values. Among them, Longzhaoshan basalt is characterized by loss of K, trace enrichment or trace loss of Ti, while Ertan basalt is characterized by trace enrichment of Ti and loss or enrichment of K and Ba.
The characteristics of trace elements cobweb diagram of fine gabbro (vein) in Longzhaoshan are similar to those of basalt in Longzhaoshan (Figure 4-24).
In addition, the contents of Rb, Ba, Th, K, Ta and Nb in picrite basalt at the bottom of Xinjie rock mass are relatively low, which is roughly equivalent to the sample with the lowest content in Longjiaoshan basalt, but the content of Ti is relatively high, which has obvious enrichment characteristics. On the other hand, the abundance value of alkaline basalt andesite at the top of Xinjie rock mass is generally similar to Ertan basalt, but it is rich in Th, La, ce and Hf, while Ba and Sr are deficient (Figure 4-24e).
The trace element distribution curves of Qingshuihe rock mass and Dayanzi rock mass are very similar (Figure 4-24b and Figure 4-24d), showing that Hf is relatively rich, Sr is strongly depleted, P and Nb are depleted, and Ti is slightly depleted. The content of incompatible trace elements in peridotite is generally lower than that in gabbro.
Fig. 4-24 Spider web diagram of trace elements in basic-ultrabasic rocks and Emeishan basalt in Panxi area.
(The original mantle value is based on Sun-mcdonough,1989; According to the data of Hongge rock mass, Hu Sufang, 2001; According to Hong Zhong, data of Ertan basalt and some Longjiao Mountain basalts are available in 2006.
There are also some differences in chemical composition between the two rocks: the low-field elements Rb, Th and U are highly enriched in Qingshuihe rock mass. However, the potassium content in 1 neutral gabbro sample is particularly low, resulting in low Rb content and obvious potassium loss; Other samples showed no abnormality in potassium, but negative abnormality in Ba (Figure 4-2 1b). Dayanzi rock mass is rich in Th and U, with obvious loss of K, and the abnormal characteristics of Ba are not obvious on the whole (Figure 4-2 1d).
Hongge rock mass and Xinjie rock mass are very developed due to magmatic crystallization differentiation, which makes the composition of trace elements in the rock mass very complicated. Generally speaking, these layered rocks are characterized by obvious enrichment of titanium and low field strength elements (Figure 4-2 1e and Figure 4-2 1f). Among them, the contents of titanium and phosphorus in Hongge rock mass are particularly rich, and the contents of Rb, Ba and Th in some peridotite or pyroxenite are very low, while in some rocks containing gabbro or pyroxenite, the abundance values of normalized thickness of original mantle of Ta, Nb, La, ce and Sr in many rocks are relatively high, and these elements have no obvious abnormal characteristics as a whole.
The enrichment degree of titanium in Xinjie rock mass is not as high as that in Hongge rock mass, and most composition points also show the enrichment of U and the negative anomaly characteristics of P, Nb and Sr (Figure 4-2 1e).
The overall characteristics of chemical composition of different rock bodies in Panxi area and basalt in Emei Mountain can be roughly reflected from Figure 4-25: the chemical composition of Dayanzi rock body is very similar to that of Qingshuihe rock body (Figure 4-25a), characterized by Sr loss, Zr and Hf enrichment and weak negative titanium anomaly; The difference is that the k and Rb of Dayanzi rock mass are low. The trace element compositions of Hongge and Xinjie plutons containing vanadium-titanium magnetite are obviously different from those of Dayanzi and Qingshuihe plutons, which are characterized by low content of incompatible trace elements and obviously rich in titanium. The differences between the two rock masses are as follows: Xinjie rock mass is rich in U and Th, but deficient in Nb and P, showing more shell-loving components; In addition to titanium, Hongge rock mass is also rich in P and Ta, but relatively poor in elements such as Ba, Th and U, that is, rich in refractory components (Figure 4-25a).
Figure 4-25 Spider Web Diagram of Trace Elements in Basic-ultrabasic Magma Distribution Area
(The data in the figure is geometric average, and the original mantle value is based on Sun & mcdonough, 1989).
Emeishan basalt in Xinjie area is characterized by low content of low field strength elements (rubidium, barium, thorium, uranium, potassium, etc.). ), the low U and Th contents reflect the characteristics of picrite basalt in the sample (Figure 4-25b). The u and Th contents of Xinjie rock mass and Xinjie basalt are complementary to some extent, which reflects the close genetic relationship between them.
Generally speaking, the rock mass containing copper, nickel, PGE is significantly different from the layered rock mass rich in iron, titanium and vanadium in trace element composition. The former is characterized by being rich in incompatible elements (especially low field strength elements), with a loss of Sr and a slight loss of Ti. The latter is characterized by significant enrichment of titanium and low content of low field strength elements. The differences in these characteristics show that there are significant differences in the original magma composition of these two types of rocks.
Three. Characteristics of ore-forming elements
The ore-bearing properties of different rocks in Panxi area are obviously different. Statistics show (Table 4-9) that in rocks with relatively small Cu/Ni ratio, such as Limahe rock mass, Qingshuihe rock mass and Hongge rock mass rich in vanadium-titanium magnetite, the PGE content is generally low and the Cu/Pd ratio is high; However, PGE may be better enriched in rocks with high Cu/Ni ratio, such as Dayanzi deposit, Xinjie deposit and Walnut tree deposit, which show relatively low Cu/Pd ratio.
Table 4-9 Mineralization Characteristics of Platinum Group Elements Rock Mass Containing Copper and Nickel Sulfides in Panxi Area
Yao Jiadong et al. (1988) showed that the content of (Pt+Pd) in walnut was positively correlated with Cu and Ni, but the correlation was slightly poor. When the Cu/Ni ratio in the ore is greater than 1, the platinum group elements are best mineralized.
The enrichment of Cu-Ni PGE in magmatic rocks is usually related to the alkalinity of magmatic rocks, and the abundance in ultrabasic rocks is generally much higher than that in basic rocks. For example, the contents of Cu, Ni and PGE in olivine pyroxenite in Dayanzi rock mass in Huili county are 3 ~ 13 times higher than those in gabbro and gabbro.
There is a good positive correlation between the content of (Pt+Pd) and the content of Cu in Dayanzi deposit in Huili County (Figure 4-26a), which also conforms to the law of the enrichment of platinum group elements in copper-bearing sulfide. However, the positive correlation between (Pt+Pd) and Ni content is not significant enough (Figure 4-26b). The correlation diagram of Au and (Pt+Pd) content (Figure 4-26c) shows that Au is mineralized together with copper sulfide and platinum group elements, while gold in dolomite seems to be mineralized alone.
Although the Cu/Pd ratio and Pt/Pd ratio of Dayanzi deposit vary greatly, the Pt/Pd ratio of most samples is between 1.5 ~ 5, and the Cu/Pd ratio is mainly near the original mantle ratio, indicating that platinum group elements are highly enriched in copper-bearing sulfides.
The spatial distribution of copper, nickel, PGE and other ore-forming elements in borehole ZK30 1 in Xinjie rock mass is studied in detail. The analysis values of ore-forming elements are shown in Table 4-6 ~ Table 4-8 and Table 4- 10.
Xinjie rock mass controlled by ZK30 1 drilling in Xinjie mining area is equivalent to the first accumulation cycle of rock mass (Figure 4- 1 1), and the roof and floor of rock mass are all basalt. Light (thin) film identification and petrochemical composition analysis show that rocks with high sulfur content are not rich in platinum group elements, while ultrabasic rocks rich in platinum group elements are not rich in sulfide. This shows that the enrichment degree of platinum group elements in sulfide is very different.
Because Xinjie rock mass tends to the southwest and has a steep dip angle, although the rhythmic bedding of rock mass is obvious, it still fluctuates greatly in space. Usually, a borehole can only control part of the lithofacies zone of rock mass. In order to investigate the spatial variation of ore-forming elements in the whole rock mass, it is necessary to comprehensively study the borehole data. As shown in Figure 4-27, the spatial lithology characteristics of four lithofacies zones of ZK 10 1 and ZK 104 Xinjie rock mass.
Figure 4-26 Relationship diagram of ore-forming elements in basic-ultrabasic rocks and mineralized dolomite in Dayanzi mining area
Table 4- 10 Table of Mineral Element Composition of Borehole ZK30 1 Xinjie Mining Area
sequential
Note: According to the analysis of southwest metallurgical geological test, the contents of Pt, Pd and Au are 10-9, Ag is 10-6, and Cu and Ni are 10-2.
At the exploration line 1 of Xinjie rock mass, Pt, Pd, Os, Ir and Ru are enriched in peridotite (1a) and peridotite-bearing (1b) lithofacies belts at the bottom of the rock mass (Figure 4-28). The contents of Cu, Ni and S in the first lithofacies zone (5 samples) with good mineralization of platinum group elements are high, indicating that the mineralization of platinum group elements is related to copper-nickel sulfide; Both samples have obvious positive europium anomalies (Figure 4-28), indicating that there may be a small amount of early crystallized plagioclase in peridotite. At the mineralized site, the Cu/Pd ratio of 1 sample is less than the original mantle value (Figure 4-28), and the Cr content of the rock is only 0. 1 1% (Table 4-7), suggesting that platinum group elements may be highly enriched in sulfide.
Figure 4-27 Schematic Diagram of Xinjie Rock Exploration Line 1 Sampling Location
In addition, the content of Pt+Pd in Xinjie rock ZK 18 1 borehole (containing pyroxenite) is 1.5g/t, and the content of Os+Ir+Ru is 0.094g/t. ..
Fig. 4-28 Variation trend of borehole ore-forming elements and geochemical parameters in Xinjie rock mass ZK10104.
● ultrabasic rocks; ◆ Basic rocks; ▲ basalt
Fig. 4-29 Profile of Ore-forming Elements Content and Geochemical Parameters in Xinjie Rock Mass ZK30 1 Borehole
● ultrabasic rocks ◆ basic rocks; ▲ basalt
To sum up, a small amount of sulfide fluid rich in platinum group elements melted from magma and sank into peridotite facies at the bottom of Xinjie rock mass, forming the first lithofacies zone containing platinum group elements.
According to the data of Panxi geological team, the borehole ZK30 1 in Xinjie rock mass is controlled to be 387.06 meters deep, and two layers of platinum group element mineralized bodies are found at 28 1.32 ~ 284.02 meters and 286 ~ 293.22 meters, with average contents of Pt+Pd of 0.87g/t and 0.36g/t respectively.
According to the results of our sampling analysis (Table 4- 10), the average contents of Pt+Pd in the range of 280.5~285m and 29 1 ~ 294m are 0.33g/t(4 samples) and 0.26g/t(2 samples), respectively, which shows that the analysis results of the two are basically consistent (. The content of chromium is low, which is positively correlated with the content of platinum and palladium. The negative europium is obviously abnormal (δ EU 0.52 ~ 0.77). ② Lower coal seam (29 1 ~ 294m): Ni content is relatively low, Cr content is high, and there is no europium anomaly (δ EU 0.88 ~ 0.89).
Generally speaking, when the Cu/Pd ratio is equal to or less than the original mantle value, Pt and Pd mineralization will occur (Figure 4-29), which is consistent with the geochemical characteristics of some typical platinum group element deposits in the world (James E.Mungall, 2005); From another point of view, the place where the ratio of (Pt+Pd)/Cu of basic rocks suddenly increases is also the place where platinum group elements are mineralized.
From Figure 4-28, it can be concluded that the content of Pt+Pd is closely related to the ratio of Pt/Pd (approximately positively related). In the mineralized parts of platinum and palladium, the content of platinum is often higher than that of palladium, while in areas with low platinum group elements, the content of platinum is lower than that of palladium.
Gold and silver tend to be enriched near the contact zone at the bottom of rock mass (Figure 4-28). Basalt infiltration is often seen in these positions, and the rocks are generally broken, with traces of hydrothermal activity.
Copper, nickel and sulfur have obvious positive correlation. They are rich in copper-nickel sulfide and tend to be concentrated in the lower part of the rock mass (the first rhythmic cycle). The Cu/Ni ratio gradually decreases from the bottom to the top of the rock mass.
To sum up, the mineralization of platinum group elements in Xinjie rock mass meets the following conditions:
The mineralization of (1)PGE in peridotite phase (the content of Pt+Pd is 0.05 ~ 0.2g/t) is related to the high content of sulfide, which is formed by molten sulfide sinking into early crystalline peridotite phase. However, in some samples with high sulfide content, PGE content is not high.
(2) The sulfide content of samples with Pt+Pd content greater than 0.2g/t is often lower. At this time, there are two different situations. One is that the Cr content and Cu/Ni ratio are relatively low, and there are mineralization sites with negative europium anomalies, which belong to the late stage of differential crystallization. Trace sulfides are crystallized from magma due to S saturation, which is caused by high concentration of platinum group elements; The other is PGE-rich site, with high Cr content, no europium abnormality, and trace sulfide rich in platinum group elements.