The idea that most of the lager deposits were formed by smaller intrusion was firstly proposed on the basis of much prospecting practice in 1979. Through a long term of theoretical researches and guiding prospections， many large and super large deposits have been discovered， so the thought was accepted by more and more scholars. By summarizing the conception， connotation and category of the theory for large deposits formed by smaller intrusion， this paper pointed out that the five key features of this theory are “small， wide， large， high and shallow (potential)”. Through many studies on the ore genesis， we developed the idea of the large deposit formed by smaller intrusion into a theory， and presented metallogenic models， metallogenic mechanisms and metallogenic types for two kinds of large deposit formed by smaller intrusion. One kind is the deposit formed by mafic magma which has experienced deep segregation (preconcentration) at first， then emplacement by pulses and finally concentration into a deposit in the terminal of magma chamber； the other kind is the deposit formed by intermediate-acidic magma， which is presented as mineralization at the head of intrusion (mineralization at the head of gas， liquid， mineral， fluid)， and mineralization in the front of intrusion and lateral space.
This article summarized the main metallogenic tectonic settings of the magmatic Cu-Ni (PGE) deposits in China by the regional distribution characteristics， new progresses in exploration， and new research materials. It found out four important metallogenic tectonic settings which were large igneous province， rift on craton margin or intracontinental extensional environment， post-collisional extensional environment on orogenic belt， and active continental margin or island arc. Comparing the findings with other countries， the result showed that China lacks the magmatic sulfide deposits related to greenstone belt and ophiolite belt， but the large scale mineralization in the post-collisional extensional environment on the orogenic belt is quite rare in the world. Therefore， the prospecting direction should fully consider those small mafic-ultramafic intrusions which related to the four types metallogenic tectonic settings mentioned above.
The theory on small intrusions forming large deposits put forward by academician Zhongli Tang was a recapitulative summary by Long-term studying of magmatic Ni-Cu sulfide deposits which related to mafic-ultramafic intrusions. And this theory got a common response by exploration industry in the world. Many mineral exploration practices have effectively illustrated that the hypabyssal and small intrusion could always form the larger ore deposits. Our study is about the mineralization of Ni-Cu sulfide deposits which related to mafic-ultramafic intrusions in the northwestern of China. In this paper，we have discussed the theory of small intrusions forming large deposits，considering that mantle magma deep part liquation and injection is the main mechanism of this theory. And another theory of magma conduit systems，may cause the local enrichment of mineral，and like that theory of small intrusions forming large deposits. After summarizes the prospecting fact of magmatic Ni-Cu sulfide deposits in the northwestern of China，we expand the scientific connotation of the theory on small intrusions forming large deposits，and make it more realistic meaningful in guiding prospecting.
“Known for unknown” is an important guiding ideology and prospecting method in mineral exploration and a work based on the known clues for prospecting. “Known for unknown” discuss relative to the prospecting for new working target，mainly in space layout and the difference between the point and the surface and the unknown regions and known ore deposits，and put forward prospecting method to analysis of development theory in “Known for unknown”. And then promote and determine “Known for unknown” theory in ore prospecting work in practical the route.
The resources of nickel and platinum group element (PGE) are contributed by super-large scale magmatic Ni-PGE sulfide deposits in the world. In this paper， on the basis of the behaviors of Ni， Cu and PGE in the processes of partial melting， magma crystallization and sulfide segregation etc. mantle magmatic events， we summarized the types and scales of ore-forming magma， the gathering way of ore-forming metal elements， the controlling factors of sulfur saturation and the immiscibility of the sulfide liquid phase during the magmatism of Ni-Cu-PGE sulfide deposits， and discussed the role of volatiles in the transport and enrichment of ore-forming metals. It is concluded that the high degree of partial melting (i.e.， magma with high Mg content) in mantle is crucial to gather the huge amounts of Ni and PGE from mantle sulfide and olivine into ore-forming magma， and the sulfide segregation will form super-large scale Ni-PGE sulfide deposits in a large scale layered (or conduit) intrusion. It is inferred that the supercritical fluid (volatile) in mantle can carry and aggregate a large number of Ni-PGE metals from a large volume of mantle， and make a great contribution to the formation of Ni-PGE sulfide deposits. It is possible to be the metallogenic mechanism of magmatic Ni-PGE sulfide deposits by small mantle derived magma (i.e.， small intrusion).
The felsic rock mass always enrich Cu，Mo，W，Sn，Nb，Ta ，then become an rare and non-ferrous metals deposit.Most of these rock masses are small（area＜10 km2）. High SiO2， K2O， K2O/Na2O are benefit of enriching Mo in the magma which rock mass enriches Cu， Mo；high Al2O3， Fe2O3T， MgO， CaO are benefit of enriching Cu in the magma which rock mass enriches Cu，Mo.High SiO2， K2O are benefit of enriching W in the magma which rock mass enriches W， Sn；high Al2O3， Fe2O3T， MgO， CaO are benefit of enriching Sn in the magma which rock mass enriches W，Sn.High Fe2O3T， alkali，TiO2 and low P2O5 are benefit of enriching in the magma which rock mass enrich Nb， Ta. The enriching Cu of rock mass is S type granite，but the enriching Mo of rock mass is transiting from I type to S type granite；the enriching W， Sn of rock mass is S type granite； the enriching Nb， Ta of rock mass has A type， I type and S type granites.
The samples were collected from Jinchuan continental scientific drilling core of 1 000 meters below.The geochemical analysis of variational basalts show that the distribution patterns of the rare-earth element(REE) were rich in light REE and the light and heavy REE fractionation significantly right mode. Trace elements show Rb， Ba， La， Ce， Nd， Sm， Nb， Ta are relative enrichment and Sr， Zr ， Hf are deficit. High Nb/Yb ratio， Th/Ta=1.7~5.63， Ta/Hf=0.10~0.21 ，which shows that the characteristics of continental rift basalt in the early time. We can conclude that Paleoproterozoic Longshoushan block is in the initial stage of continental block cracking. Zircon U-Pb isotopic ages indicate that the Longshoushan Block Baijiazuizi Group experienced at least three intense tectonic magmatic metamorphism event， period of peak events are respectively 2.1 Ga， 1.9 Ga and 1.85 Ga. Contrast of the tectonic evolution and stratigraphic structure of the Longshoushan block and North China plate， Yang Zi plate， Tarim plate and Western China Craton， we know that Longshoushan block has most similarities with Western China Craton. So the prospecting orientation for the Cu-Ni sulfide deposit in the future should be put in the whole Western China Craton.
By the using of geochemical methods and quantitative textural analysis，This paper studied the spatial distribution characteristics of platinum group elements in Jinchuan Ni-Cu-（PGE） sulfide deposit，discussed the dynamic behavior in the process of magma evolution，and the evolution of Jinchuan mafic-ultramafic magma .This study found that the spatial distribution of the platinum group elements showing a certain regular changes between four continuous ore bodies. Overall，there are a significant decrease in the value of Pd/Ir-Ni/Cu between the four ore bodies from west to east. Through?the analysis，the cause which effected the distribution is that the monosulfide solid solution（MSS） has experienced a process of crystallization differentiation during crystal fractionation. On the other hand，through quantitative textural analysis，found that the structure of No. 1 ore body is much more mature than No. 1 ore body，which suggested that the emplacement of the former one is much more earlier than the latter one. Integrated geochemical and magma dynamics information，finally obtained the conclusion that the moving direction of Jinchuan magma conduit system is along the strike of the intrusions from northeast to southeast.
According to the analysis and comparison with the content and geochemical characteristics of and trace element from Cu-Ni sulfide deposits between Kelatongke and Jinchuan， meanwhile， combing different tectonic setting and rock series of these two types of deposits， we study their magmatic and mineralization processes. The results show that major element of Kalatongke belongs to the tholeiitic basalt system； incompatible trace element presents as enrichment of large ion lithophile elemen(LILE) and depletion of high field strength element(HFSE)， suggesting that they are derived from the continental crust； the rare earth element (REE) presenting rich in light rare earth element (LREE)， and there is no obvious Eu anomalies， Sr and Nd isotopes indicates that the magma source is depleted asthenosphere mantle. Major element of Jinchuan deposit belongs to the tholeiitic basalts and mid ocean ridge basalt system； incompatible trace element presents as enrichment of LILE， depletion of HFSE， showing the magma suffers from contamination of crust materials or there are materials of subducted oceanic crust in the source ； the ratio of N(La)/N(Nb) and N(Zr)/N(Nb) indicating its source is derived from EMI mantle； the REE presenting enriched in LREE， the ratio of N(La)/N(Yb)， N(La)/N(Sm) and N(Gd)/N(Yb) presenting enriched in LREE； and there is no obvious Eu anomalies， Sr and Nd isotopes declaring magma derived from enriched mantle. And we also predicted the magma conduit and mineralization potential of two ore deposits by 3D geological modeling， hoped it will useful for later period exploration.
A number of small and medium Au and Cu deposits （occurrneces） were found in Guaizihu area， Inner Mongolia， and these deposits were accompanied by small granite strains （branch） in spatial terns. This paper， using petrogeochemistry method and combining the study of macropetrology in the field， revealed the internal relationship of magma source area qualities and mineralization. The results showed that Guaizihu granite belongs to high-K calc-alkaline series with peraluminous characteristics， relatively strong fractionation between light rare earth element（LREE） and heavy rare earth element（HREE）， and relatively enriched in LREE （（La/Yb）N=3.78～20.13）. ORG normalization of trace elements showed that the granites are enriched in large-ion lithophile elements（LILE） such as Rb，Ba，Th，K and depleted high field strength elements（HFSE） such as Nb、Ta、Sr、P . Guaizihu granite belongs to low Sr and low Yb type. The magmatic source is from lower crust volcanic rock. The magma formed in lower crust partial melting which is induced by the process of collision orogenic - crustal thickening. A series of evidence showed that the disappearing of ancient Asia ocean in the east of Central Asian orogenic belt， which is represented by Engel Usu ophiolite belt， occured at the end of the early Permian.
The magmatic Cu-Ni sulfide deposit is mainly hosted in mafic-ultramafic intrusions which are generally small scales. The ore body is mainly hosted in the base of the intrusion. This forms a large number of deposits which we call “mall intrusion forming large deposit”. In the world，there are many mafic-ultramafic intrusions，but how to determine the metallogenic potential of intrusion has been concerned all the time. In this paper，based on previous studies，we take eastern Tianshan as an example，compare and analyze the geological and geochemical characteristics of the economic mineralized mafic-ultramafic intrusions and the uneconomic mineralized mafic-ultramafic intrusions，in order to distinguish the metallogenic potential from theory. The prospecting evaluation indexes are gained from this study，mineralized mafic-ultramafic intrusions are generally characteristic by right incline in Chondrite normalized REE pattern diagrams；several stages of magma intruding are important；a certain amount of orthopyroxene is contained in the rock；the mineral grains are obviously different， et al.