Geochemical Features and Mineral Associations of Di ﬀ erentiated Rocks of the Norilsk 1 Intrusion

: The purpose of this study is to show the patterns of distribution of disseminated sulﬁde in layered rocks based on the numerous geochemical and mineralogical data obtained for eight boreholes of the Norilsk intrusion (southern part of the Norilsk 1 deposit). There is a common trend of sulﬁde liquid fractionation in the Main Ore Horizon, which is composed of picritic and taxite (or olivine) gabbro-dolerites: the Ni / Cu in both rock types decreases down all sections, indicating an increase in the degree of fractionation of the sulﬁde liquid from top to bottom. On the contrary, the Ni / Fe ratios in pentlandite increase in this direction due to an increase in sulfur fugacity. However, picrite and taxite / olivine gabbro-dolerites are very distinctly separated by Ni / Cu values: these values are > 1 in picritic gabbro-dolerite while they are always < 1 in taxite / olivine gabbro-dolerite. These rock types are distinguished by sulﬁde assemblages. The ﬁrst includes troilite, Fe-rich pentlandite, chalcopyrite, cubanite, talnahite, bornite and copper (low sulfur association); the second one is composed of monoclinic pyrrhotite, chalcopyrite, Ni-rich pentlandite and pyrite (high sulfur association). A two-stage magma injection with di ﬀ erent ore specializations is supposed for picritic and taxite / olivine gabbro-dolerites.


Internal Structure of the Norilsk 1 Intrusion in Its Middle Part
Boreholes intersected the following rocks from top to bottom: tholeiitic basalts of the Nadezhdinsky, Tuklonsky, Khakanchansky, Gudchikhinsky and Syverminsky Suites, rocks of the upper gabbro series (leucogabbro or breccia) with a low-sulfide horizon in PH-72 and PH-222; then main gabbro series (gabbrodiorite, olivine-free, olivine-bearing, olivine and picritic gabbro-dolerite); and rocks of the lower gabbro series (taxite or olivine gabbro-dolerites, and then the contact rocks).
The disseminated sulphide mineralization is found in the low-sulfide horizon as well as picritic, taxite, and olivine (lower) gabbro-dolerites. The low-sulphide horizon differs from the disseminated ores of the layered series by the elevated PGE (ppm)/S (wt.%) ratio, which varies within the range of 5-70 ppm, and relatively low Cu and Ni contents (≤1 wt.% total), which are positively correlated with PGE (up to 60-70 ppm) [29]. Vein-disseminated ores are sometimes localized sometimes in sandstones and siltstones in the southern part of the studied cross-section, and in titanium-augite gabbro-dolerite (a moderately alkaline variety of rock) in the middle part of the cross-section.
The taxite gabbro-dolerite of the lower part of the cross-section, which is so characteristic of the Talnakh intrusion and the Norilsk 1 deposit [28], is present only in three boreholes (

Methods
The samples were collected from the cores of the exploration boreholes. We conducted the rock analyses for Pd, Pt, Au, Cu, Ni, Co, and S performed in the laboratory of the Stewart Geochemical and Assay LLS, Moscow using the inductively coupled plasma atomic emission spectrometry (ICP-AES) by assay analysis after dissolution in a mixture of acids (codes ME-ICP61 and PGM-ICP23). The Method is sensitive for Au, Pd-0.01-10 ppm, Pt-0.05-10 ppm; Co, Ni, Cu-1-10,000 ppm, S-0.01-10%.
In addition, about 80 combined samples of various compositions of gabbro-dolerites were analyzed for all PGE (including Os, Ir, Ru) in the Testing and Analitical Center for quantitative chemical analyses of Gipronickel Institute LLC using the method of inductively coupled plasma mass spectrometry (ICP-MS), with a preliminary content of these elements on nickel matte. A sample of matte is dissolved in hydrochloric acid, and nitric acid is added to the solution. In this case, the insoluble precipitate is additionally dissolved with moderate heating. The content of noble metals is measured in the solution. The "iCAP-Qc" from the Thermo Fisher Scientific corporation and atomic absorption spectrometry ("iCE 3000 Series") with a reaction-collision cell are used to suppress spectral overlaps to eliminate polyatomic overlaps from matrix elements (Cu, Ni). Numerous (about 1000) EDS analyses were performed in the Norilsk Nickel R&D Center in the Siberian Federal University on a Tescan Vega 3 SBH instrument (Oxford X-Act EMF analyzer), Krasnoyarsk. The probe size was 270 nm, the accelerating voltage 20 kV.
The wavelength dispersion spectrometry (WDS) analyses of sulfides for testing the EDS data were performed with a JEOL JXA-8100 electron microprobe in the Analytical Center of Multi-Elemental and Isotope Research of the VS Sobolev IGM of the SB RAS, Novosibirsk (Karmanov Head). The accelerating voltage is 20 kV; the probe current is 30-50 nA over the surface of the specimen for both sulfides and PGM; the probe diameter is~1 µm. The duration of measurement is 20 s for each analytical line. The overlapping of elements in the X-ray spectra was evaluated using the OVERLAP CORRECTION software. Analytical conditions are shown in Table 1. The contents of elements were calculated with the XPP program for the microprobe software. The accuracy and reproducibility of the analytical procedures were evaluated with special tests [35].

PH-14
A schematic column for the interval of the Main Ore Horizon in borehole PH-14 is shown in Figure 3. This interval includes the picritic and taxite gabbro-dolerites, vein-disseminated ores in the lower part of the section, and sedimentary rocks. A 36-m thick chromite horizon has been identified in the picritic gabbro-dolerites on the basis of abundant chromian spinel (CrCp). The chromite horizon is delineated from the finding of chromian spinel in polished samples (in reflected light). Cr-Sp occurs as a dissemination of small isometric grains, which are included in both silicate minerals and sulfides. Cr-Sp grains are unevenly distributed in the chromite horizon: from single grains among sulfides to dense dissemination, when chromite makes up 3 vol %. The compositions of chromites in the picrite gabbro-dolerite vary very widely [30]. They are confined to the lower part of picritic gabbro-dolerite and are in contact with olivine gabbro-dolerite. Nickel prevails over copper over almost the entire range of picritic gabbro-dolerites: the average Ni/Cu value is 1.24. Positive anomalies of Pt and Pd are observed in the chromite horizon, where a predominance of copper over nickel is observed (Figure 3a).
The opposite pattern is observed in olivine gabbro-dolerite: copper prevails over nickel: the average Ni/Cu value is 0.69. The levels in which Ni/Cu > 1 are also present in these rocks, which coincide with vein-disseminated ores containing a high content of Pd (up to 6.5 ppm), Pt (up to 4 ppm), and S (15 wt.%) (Figure 3a). The Ni/Cu ratios decrease with depth in general. Palladium prevails over platinum in the entire range of picritic and olivine gabbro-dolerites. The ratio of Pd/Pt as a whole increase downward along the cross-section: Pd/Pt = 2.5 (on average) in the upper part of picritic gabbro-dolerite (with CrSp), 2.8 in the lower part, 3.0 in olivine gabbro-dolerite, and 4.4 in vein-disseminated ores [33]. Vein-disseminated ores are phenocrysts of sulfides and their accumulations (schlieres) appear in irregular shape up to 50 mm in size, which make up between 5% and 60% of the rock volume. Sometimes, there are veins of massive ores 20-cm thick. The cross-section of the PH-14 borehole is similar to the northern intrusive body (OM-4) of the Maslovsky deposit ( Figure 1) [3].

PH-72
The schematic column for borehole PH-72 includes taxite rocks of the upper gabbro series, olivine, picritic, taxite, contact gabbro-dolerites, and vein-disseminated ore in titanium-augite basalt (basalt of of moderate alkalinity). The analysis of ore elements and sulfur is shown in Table 2 as an example. The low-sulfide horizon is observed in the upper gabbro series at a depth of 609.7-612.1 m. It is characterized by low contents of Cu (up to 0.10 wt.%), Ni (up to 0.08 wt.%) and S (up to 0.44 wt.%), and elevated contents of PGE (Pd + Pt up to 8.19 ppm). Pd prevails over Pt, and Cu over Ni in this horizon (Figure 3b).
The Ni/Cu ratios gradually decrease down the section from olivine (2.87 on average) to picritic (1.08), to taxite (0.66), then to contact gabbro-dolerites (0.48), again increasing slightly in exocontact ores (0.66) (Figure 3b). The Pd/Pt ratios, on the contrary, increase in this direction from 2.08 (average) in olivine gabbro-dolerite to 2.69 in the exocontact ore. The relatively high contents of PGM (Pd + Pt is 2-8 ppm) have been noted in the chromite horizon, which was identified at the bottom of picritic gabbro-dolerite. Contents of Pd and Pt increase in taxite gabbro-dolerite, reaching 7.69 ppm and 3.12 ppm, respectively. These contents are even higher in the ores: Pd is 10 ppm, and Pt is 3.5 ppm (Figure 3b).

PH-133
The schematic column for borehole PH-133 includes picritic and taxite gabbro-dolerites, a thin horizon of densely disseminated ores in the lower part of taxite gabbro dolerites, mudstone and Ti-augite dolerites (Figure 3c). A chromite horizon with a thickness of more than 60 m has been identified in picritic gabbro-dolerites. It is confined to the lower part of the picritic gabbro-dolerites. Nickel prevails over copper in almost the entire range of picritic gabbro-dolerites ( Figure 3c): the average value of Ni/Cu is 1.24. In this interval, there are several points with a predominance of copper over nickel, which coincide with the Pt-Pd anomalies. Down the picritic gabbro-dolerite section, the Ni/Cu ratios decrease and, finally, they become less than one near the contact with taxitie gabbro-dolerite, in which the average Ni/Cu value is 0.61. Palladium prevails over platinum over the entire interval of rocks of borehole PH-133. The Ni/Cu and Pd/Pt ratios correlate negatively in picritic gabbro-dolerite (the palladium content increases with a decrease in the nickel content), while such a regularity does not occur in taxite, contact gabbro-dolerites and mudstones ( Figure 3c).

PH-193
Olivine gabbro-dolerite (main gabbro series) of borehole PH-193 has low contents of all ore elements (Cu does not exceed 0.01, Ni 0.07 wt.%, Pt + Pd-0.03 ppm). The ratios of Ni/Cu are 6-7. The content of Ni reaches 0.34 wt.%, Cu 0.40 wt.%, and Pt + Pd 3.05 in picritic gabbro-dolerite. In general, nickel prevails above copper: the Ni/Cu ratio is 2.6 (average). The chromite horizon was not intersected in the picritic gabbro-dolerite of borehole PH-193 ( Figure 3e). Copper (up to 0.32 wt.%) prevails over nickel (up to 0.22 wt.%) in the lower olivine gabbro-dolerite: the Ni/Cu ratios are 0.58 on average. The total content of Pd + Pt reaches 3.13 ppm. The vein-disseminated ore with a thickness of about 10 m is located at the contact with sandstone. The content of Cu reaches 3.19, and Ni 1.04 (wt.%), and Ni/Cu is 0.5 on overage, Pd + Pt-20.0 ppm (Figure 3e). The Pd/Pt ratios vary significantly in the olivine gabbro-dolerite, but, in general, they increase down the section, while the values of Ni/Cu decrease smoothly.

PH-222
A schematic column for borehole PH-222 is shown in Figure 3f. It includes two intervals: the first interval is composed of feldspar and labrador basalts and breccias with a low-sulfide horizon; the second Minerals 2020, 10, 688 6 of 22 interval includes picritic, olivine, contact and titanium-augite gabbro-dolerites with a horizon of vein mineralization. Nickel prevails over copper only in the low-sulfide horizon of the upper gabbro series and in picritic gabbro-dolerites (Ni/Cu is 1.35), intensively decreasing down the section; the Ni/Cu ratios are less than 1 in olivine, contact and in Ti-augite gabbro-dolerites (0.54, 0.63 and 0.17, respectively). Palladium significantly prevails over platinum in picritic, olivine gabbro-dolerites and in vein ore (the Pd/Pt ratios are 3.16, 2.79 and 2.63, respectively), while the content of Pt prevails over Pd in basalts, contact and Ti-augite gabbro-dolerites, where the absolute contents of noble metals are very low. The amounts of Pt and Pd reach almost 9 ppm in the vein ore. The contents of Pd + Pt and S in disseminated ores hosted in picritic and olivine gabbro-dolerites show a positive correlation.

PH-243
A column for borehole PH-243 includes picritic, olivine and contact gabbro-dolerites (Figure 3g). A 12.8-m thick chromite horizon located in the middle part of picritic gabbro-dolerite has been distinguished. Nickel prevails over copper in picritic gabbro-dolerite; the average value of Ni/Cu is 1.40, but, in the chromite horizon, copper prevails over nickel (Ni/Cu is 0.81 on average). The PGE anomalies are confined to the chromite horizon (Pd + Pt in total reaching 5 ppm) and the bottoms of picritic gabbro-dolerites. The chromite horizon divides the picritic gabbro-dolerite into two rhythms, in each of which the Cu contents increase down the section. Copper prevails over nickel in olivine gabbro-dolerite: the average value of Ni/Cu is 0.68. Palladium prevails over platinum throughout the studied section. The Pd/Pt value varies from 2 to 4 (2.28 on average) in picritic gabbro-dolerite, gradually increasing down the section, and varies significantly from 1 to 7 (average 2.65) in olivine gabbro-dolerite.

Mineralogy and Geochemical Features of Sulphide Mineralization in Various Types of Rocks
A low-sulfide horizon (borehole PH-72, 607-613 m) is located in the gabbro series at the top of the intrusion (Figure 3b). The contents of Cu and Ni are insignificant (0.06-0.18 wt.% in total), while Pd and Pt in total reach 9 ppm in the low-sulfide horizon. Monoclinic pyrrhotite is characteristic of this horizon: Fe 0.92 Ni 0.01 S 1.08 (Table 3). Pentlandite is nickel rich and constantly contains up to 5.48 wt.% of Co: (Fe 3.66 Ni 4.59 Co 0.73 ) 8.98 S 8.02 . Sperrylite, ferrous platinum, and As-bearing atokite were found in the low-sulfide horizon of borehole PH-72.
Picritic gabbro-dolerite is located below the olivine gabbro-dolerite and is characterized by variable thickness (from13 m in PH-72 to 70 m in PH-133) ( Figure 3). This rock is observed in all cross-sections. The contents of ore elements as a rule does not exceed: Cu 0.7 wt.%, Ni 0.5 wt.%, Pd 5 ppm and Pt 2 ppm. However, the ore anomalies are observed within the chromite horizons: Cu-6 wt.%, Ni-2 wt.%, Pd and Pt up to 10 ppm (Figure 3h). In almost all the intervals of picritic gabbro-dolerite, the content of nickel prevails over copper (the average value of Ni/Cu is 1.24 in PH-14). An intensive decrease in the Ni/Cu ratios occurs in the upper horizons of picritic gabbro-dolerites; then, these ratios gradually decrease in the lower contact of these rocks (Figure 3c-f). In turn, the Pd/Pt ratios, on the contrary, increase down the cross-sections. The picritic gabbro-dolerite is divided by a chromite horizon into two geochemical rhythms in some cases, in each of which these trends are repeated. This is mostly evident in borehole PH-243 ( Figure 3g). The droplet-like, irregular and interstitial sulfide aggregates up to 5 mm are characteristic of picritic gabbro-dolerite (Figure 4a  All the names of rocks are given according to the classification adopted by production geologists in the description of the Norilsk deposits, and according to Novageo LLC. "Ti-Augite" suggests that the rock belongs to the moderately alkaline series.  g-d-gabbro-dolerite, CrSp-chromian spinel. All the names of rocks are given according to the classification adopted by production geologists in the description of the Norilsk deposits, and according to Novageo LLC. "Ti-Augite" suggests that the rock belongs to the moderately alkaline series. Magnetite is common there (Figure 4a), the amount of which is negatively correlated with the amount of chromian spinel in the chromite horizons of these rocks and with ilmenite in the lower horizons of picritic gabbro-dolerite. Pyrrhotite is most common in the upper horizons of picritic gabbro-dolerite (Figure 4b). The amounts of pyrrhotite and pentlandite decrease with depth. Cubanite and chalcopyrite in the sulfide aggregates begin to dominate lower in the profile of the picritic gabbro-dolerite (Figure 4e). Chromian spinel is common at certain stratigraphic levels (chromite horizons) of picritic gabbro-dolerite (Figure 4a). The Cu-rich sulfides (talnakhite, bornite, chalcocite) and native copper are subordinate, but they are a typomorphic feature of the sulfide association (Figure 4c,f) in picritic gabbro-dolerite and are not characteristic of other rocks. A variety of copper-rich minerals from picritic gabbro-dolerite (PH-14) are shown in [33]. The composition of pyrrhotite is close to troilite (Fe 1.00 S 1.00 ); pentlandite is Fe rich ((Fe 5.21 Ni 3.64 Co 0.11 ) 8.96 S 8.04 ) in most picritic samples of all boreholes (Figure 5a,b; Table 3). The content of Fe predominates slightly over Cu in chalcopyrite; in this case, chalcopyrite occurs often as an exsolution texture with cubanite. When the chalcopyrite becomes less ferruginous, cubanite is not detected in the association. Pyrrhotite is gradually enriched with sulfur, and pentlandite is enriched with nickel down the borehole section.
The largest number of PGM grains is found in chromite horizons, consistent with the highest contents of Pd and Pt, which have a sawtooth distribution. PGMs are represented by numerous compounds: paolovite, atokite, rustenburgite, mayakite, menshikovite, polarite, sperrylite, tetraferroplatinum, sobolevskite, hollingworthite and kotulskite. These compounds do not exhibit common patterns in their distribution over the depth of the interval of picritic gabbro-dolerites. Native gold and Au-Ag alloys are characteristic of the lower parts of the picritic gabbro-dolerite section.
Minerals 2020, 10, x FOR PEER REVIEW 10 of 20 chalcopyrite; in this case, chalcopyrite occurs often as an exsolution texture with cubanite. When the chalcopyrite becomes less ferruginous, cubanite is not detected in the association. Pyrrhotite is gradually enriched with sulfur, and pentlandite is enriched with nickel down the borehole section. The largest number of PGM grains is found in chromite horizons, consistent with the highest contents of Pd and Pt, which have a sawtooth distribution. PGMs are represented by numerous compounds: paolovite, atokite, rustenburgite, mayakite, menshikovite, polarite, sperrylite, tetraferroplatinum, sobolevskite, hollingworthite and kotulskite. These compounds do not exhibit common patterns in their distribution over the depth of the interval of picritic gabbro-dolerites. Native gold and Au-Ag alloys are characteristic of the lower parts of the picritic gabbro-dolerite section.    chalcopyrite; in this case, chalcopyrite occurs often as an exsolution texture with cubanite. When the chalcopyrite becomes less ferruginous, cubanite is not detected in the association. Pyrrhotite is gradually enriched with sulfur, and pentlandite is enriched with nickel down the borehole section. The largest number of PGM grains is found in chromite horizons, consistent with the highest contents of Pd and Pt, which have a sawtooth distribution. PGMs are represented by numerous compounds: paolovite, atokite, rustenburgite, mayakite, menshikovite, polarite, sperrylite, tetraferroplatinum, sobolevskite, hollingworthite and kotulskite. These compounds do not exhibit common patterns in their distribution over the depth of the interval of picritic gabbro-dolerites. Native gold and Au-Ag alloys are characteristic of the lower parts of the picritic gabbro-dolerite section.    Taxite gabbro-dolerite located below the picritic gabbro-dolerite is about 10-m thick in all the studied boreholes (Figure 3b-d). The content of copper (up to 1.0 wt.%) prevails over nickel (up to 0.8 wt.%) throughout the sections of taxite gabbro-dolerite (PH-72, PH-133, PH-175); the Ni/Cu ratios are less than one (e.g., 0.57 on average in borehole PH-133), and they decrease down the cross-sections. The palladium content (2-10 ppm) prevails over platinum (0.8-3 ppm); the Pd/Pt ratios vary significantly throughout the range of taxite gabbro-dolerite.   The positive anomalies of all ore elements coincide with each other, and are associated with the localization of vein-disseminated ores (Figure 3b-d). Sulfides are represented by interstitial dissemination and schlieres up to 3 cm with a significant predominance of chalcopyrite over the other sulfides (Figure 6a-c). Pyrrhotite is more S rich (monoclinic Fe 0.94 S 1.06 ) and pentlandite is more Ni rich ((Fe 3.80 Ni 5.09 Co 0.08 ) 8.97 S 8.03 ) ( Table 3) (Figure 7a-c). Grains of ilmenite and magnetite occur as inclusions in the silicate minerals. Magnetite is also found in a secondary phase. Chromian spinel and Cu-rich sulfide are absent in olivine gabbro-dolerite. A positive correlation between the amounts of chalcopyrite and pentlandite and a negative correlation between both these minerals and the amount of pyrrhotite appear in olivine gabbro-dolerite, which also distinguishes them from picritic ones. Chalcopyrite is predominant in sulfide aggregates at the bottom of this interval (Figure 7с). Sulfides are replaced by pyrite-marcasite-magnetite aggregates and by violarite in some horizons. Pentlandite varies widely in its composition at different horizons from Ni rich ((Ni4.63Fe4.27Co0.11)9.01S7.99) to Fe rich ((Fe4.54Ni4.35Co0.12)9.01S7.99) ( Table 3), but with a significant predominance of nickel compounds (Figure 5a). The S content in pyrrhotite and the Ni content in pentlandite increase with depth. Millerite occurs in the association with Ni-rich pentlandite. PGMs are represented by merenskiite, paolovite, naldrettite, menshikovite, etc. Native gold has been identified as fine inclusions in silicates.  (Figure 7a-c). Grains of ilmenite and magnetite occur as inclusions in the silicate minerals. Magnetite is also found in a secondary phase. Chromian spinel and Cu-rich sulfide are absent in olivine gabbro-dolerite. A positive correlation between the amounts of chalcopyrite and pentlandite and a negative correlation between both these minerals and the amount of pyrrhotite appear in olivine gabbro-dolerite, which also distinguishes them from picritic ones. Chalcopyrite is predominant in sulfide aggregates at the bottom of this interval (Figure 7c). Sulfides are replaced by pyrite-marcasite-magnetite aggregates and by violarite in some horizons. Pentlandite varies widely in its composition at different horizons from Ni rich ((Ni 4.63 Fe 4.27 Co 0.11 ) 9.01 S 7.99 ) to Fe rich ((Fe 4.54 Ni 4.35 Co 0.12 ) 9.01 S 7.99 ) ( Table 3), but with a significant predominance of nickel compounds (Figure 5a). The S content in pyrrhotite and the Ni content in pentlandite increase with depth. Millerite occurs in the association with Ni-rich pentlandite. PGMs are represented by merenskiite, paolovite, naldrettite, menshikovite, etc. Native gold has been identified as fine inclusions in silicates.
Grains of ilmenite and magnetite occur as inclusions in the silicate minerals. Magnetite is also found in a secondary phase. Chromian spinel and Cu-rich sulfide are absent in olivine gabbro-dolerite. A positive correlation between the amounts of chalcopyrite and pentlandite and a negative correlation between both these minerals and the amount of pyrrhotite appear in olivine gabbro-dolerite, which also distinguishes them from picritic ones. Chalcopyrite is predominant in sulfide aggregates at the bottom of this interval (Figure 7с). Sulfides are replaced by pyrite-marcasite-magnetite aggregates and by violarite in some horizons. Pentlandite varies widely in its composition at different horizons from Ni rich ((Ni4.63Fe4.27Co0.11)9.01S7.99) to Fe rich ((Fe4.54Ni4.35Co0.12)9.01S7.99) ( Table 3), but with a significant predominance of nickel compounds (Figure 5a). The S content in pyrrhotite and the Ni content in pentlandite increase with depth. Millerite occurs in the association with Ni-rich pentlandite. PGMs are represented by merenskiite, paolovite, naldrettite, menshikovite, etc. Native gold has been identified as fine inclusions in silicates.

Geochemical Features of Rocks
1) General patterns of mineralogical-geochemical regularities exist in the distribution of ore elements along the cross-sections of all boreholes: a) the Ni/Cu ratios decrease in the rocks with depth; 2) the Pd/Pt ratios show sawtooth patterns, but, in general, they increase with depth, whereas typomorphic features are observed for each rock layer: a) Ni/Cu is more than one in picritic gabbrodolerite, whereas Ni/Cu is less than one in olivine gabbro-dolerite; b) contents of ore elements prevail

Geochemical Features of Rocks
(1) General patterns of mineralogical-geochemical regularities exist in the distribution of ore elements along the cross-sections of all boreholes: (a) the Ni/Cu ratios decrease in the rocks with depth; (2) the Pd/Pt ratios show sawtooth patterns, but, in general, they increase with depth, whereas typomorphic features are observed for each rock layer: (a) Ni/Cu is more than one in picritic gabbro-dolerite, whereas Ni/Cu is less than one in olivine gabbro-dolerite; (b) contents of ore elements prevail in taxite gabbro-dolerites compared to picritic ones (Figure 3b-d), while they are higher in picritic gabbro-dolerite than in the underlying olivine gabbro-dolerite. The positive anomalies of Cu, Ni, Pt, Pd in picritic rocks coincide with the chromite layer (Figure 3d,g,h). This testifies to the independence of the melts from which each of the ore-containing rocks crystallized.
All chondrite-normalized patterns of elements distribution (noble metals, Ni, Co and Cu in 100% sulfide) in the disseminated ores of gabbro-dolerites correlate well with each other. All the curves are characterized by a positive Pd anomaly. The content of ore elements in 100% sulfide in picritic gabbro-dolerite somewhat predominates over that in olivine or taxite gabbro-dolerites (Figure 9a,b). The pattern of ore elements in the low sulfide horizon is characterized by higher contents of Pt and Pd, and is comparable with the data on J-M Reef [36]. Chondrite-normalized patterns of PGEs from various types of rocks containing disseminated sulfide ores of the MOH (Table 4) show an upward trend zone from Os to Pd ( Figure 10). This zone has a steeper slope compared to the distribution patterns from the Great Dyke, which indicates a higher degree of fractionation of PGEs in the primary sulfide melts of Norilsk 1.

Mineralogical Features of Rocks
Iron-nickel ratios in pentlandite reflect the activity of sulfur (lgfS2) during its formation [39][40][41]. Chondrite-normalized patterns of PGEs from various types of rocks containing disseminated sulfide ores of the MOH (Table 4) show an upward trend zone from Os to Pd ( Figure 10). This zone has a steeper slope compared to the distribution patterns from the Great Dyke, which indicates a higher degree of fractionation of PGEs in the primary sulfide melts of Norilsk 1. Chondrite-normalized patterns of PGEs from various types of rocks containing disseminated sulfide ores of the MOH (Table 4) show an upward trend zone from Os to Pd ( Figure 10). This zone has a steeper slope compared to the distribution patterns from the Great Dyke, which indicates a higher degree of fractionation of PGEs in the primary sulfide melts of Norilsk 1.

Mineralogical Features of Rocks
Iron-nickel ratios in pentlandite reflect the activity of sulfur (lgfS2) during its formation [39][40][41]. The content of Ni in pentlandite increases as lgfS2 increases. The Ni/Fe ratio in pentlandite increases with depth in MOH. The variation in k = Ni/(Ni + Fe) in pentlandite from borehole PH-14 varies in the range of 0.33−0.47 in picritic gabbro-dolerite, which corresponds to lgfS2 from −12 to −11, whereas

Mineralogical Features of Rocks
Iron-nickel ratios in pentlandite reflect the activity of sulfur (lgf S 2 ) during its formation [39][40][41]. The content of Ni in pentlandite increases as lgf S 2 increases. The Ni/Fe ratio in pentlandite increases with depth in MOH. The variation in k = Ni/(Ni + Fe) in pentlandite from borehole PH-14 varies in the range of 0.33−0.47 in picritic gabbro-dolerite, which corresponds to lgf S 2 from −12 to −11, whereas the variation in k in pentlandites from olivine gabbro-dolerite varies from 0.49 to 0.57; therefore, they are crystallized under the conditions of lgf S 2 , corresponding to an interval from −10.5 to −9 [33]. The data from other boreholes also shows that pentlandite in picritic gabbro-dolerite has a higher content of Fe: k is 0.37 (PH-243), 0.45 (PH-175), 0.49 (PH-72 and PH-401) on average. Consequently, they crystallized with less S fugacity compared to pentlandites from olivine gabbro-dolerite (k is 0.52 in PH-401 and 0.47 in PH-243) or in taxite gabbro-dolerite (k is 0.48 in PH-72 and k is 0.56 in PH-175).
Thus, two different sulfide assemblages are characteristic of picritic and taxite (or olivine) gabbro-dolerites. The sequence of sulfide formation in picritic gabbro-dolerite is due to the sequential crystallization of a monosulfide solid solution (mss) and then a copper-rich residual melt, from which an intermediate solid solution (iss) was formed in the conditions of low sulfur fugacity. The solid-phase reactions with decreasing temperature led to the mss decomposition and the formation of an association of troilite, in which the plates of cubanite and Fe-rich pentlandite are present. This association then reacted then with the residual melt with an increase in the amount of cubanite up to the formation of granular species. Chalcopyrite, at this stage of crystallization was present in a sharply subordinate amount. Iss decomposed in association with chalcopyrite + Fe-rich pentlandite ± talnachite ± bornite ± cubanite ± pyrrhotite (h > m) . (h-hexagonal, m-monoclinic). These studied parageneses in picritic gabbro-dolerite are related to the "low-sulfur" minerals sequence [1].
In olivine and taxite gabbro-dolerites, sulfides are represented by a "high-sulfur" association composed of pyrrhotite (m > h) , (m-monoclinic, h-hexagonal) chalcopyrite, pentlandite (Fe < Ni) (Fe rich or Ni rich) and pyrite, which are due to the pyrrhotite-chalcopyrite fractionation in conditions of increased sulfur fugacity. At the same time, talnakhite, bornite, and native copper are absent in this assemblage. According to [4], these ores are characterized by the simple zonality of the first type. The sequence of crystallization of mineral parageneses is due to the evolution of mss and iss. When cooled, mss decomposes into monoclinic and hexagonal pyrrhotite with lamellas of chalcopyrite. According to the experimental data, tetragonal and cubic chalcopyrite and pentlandite with a high content of Ni are decomposed from iss [42]. The general sequence of sulfide formation of these ores was described by [1] based on the studies of [10,43].
Therefore, there is a clear genetic relationship between the sulfide assemblages in disseminated ores and the type of the host gabbro-dolerites. Our data show that the concentric zoning of the ores described by [4] is absent in the Norilsk 1 intrusion. In each rock layer (picritic, taxite or olivine gabbro-dolerites), the mineral associations do not change laterally, and are similar in the central part of the intrusion and in its flanks. Each of the stratigraphic layers has its own geochemical and mineral zoning from top to bottom, expressed by a decrease in the Ni/Cu ratio and an increase in the Pd/Pt ratio, the chalcopyrite share and the content of Ni in pentlandite. The general vertical zoning, despite the apparent continuity of geochemical characteristics, is actually composed of individual zoning. The apparent general zoning of the Main Ore Horizon is most likely superimposed, and the "continuity" is due to the fact that the layer underlying picritic gabbro dolerites (taxite or olivine gabbro-dolerites) was crystallized from a more fractionated silicate melt, which also contained a more fractionated sulfide liquid, from which the high-sulfur parageneses were crystallized. Since the ore-bearing horizons of the Norilsk 1 intrusion contain sulfur that exceeds its solubility in silicate magma by several times [44][45][46], it can be assumed that immiscible sulfide liquid as droplets in a silicate melt came from the mantle [47] or lower-crustal [3] chambers to the chamber of formation. The contrasting difference in the evolution of mineral paragenesis in picrite and taxite/olivine gabbro-dolerites may indicate two non-simultaneous melt pulses for these two types of mineralized rocks, providing the typomorphic features of each of the horizons. In other words, taxite and picritic gabbro-dolerites cannot be fractionated from a single melt in the formation chamber (intrusive body), but are the result of a two-stage magma injection of various melt types containing sulfide liquids of different compositions. The dissolution rates of sulfide droplets in flowing magma are slow relative to the flow rates, such that sulfide might be transported in, and deposited from, silicate magmas at distances of kms from the generation site [48]. This is consistent with the results for the U-Pb ages of zircons of the Kharaelakh intrusion (and, quite probably, others) that fit into four time intervals: 347 ± 16, 265.7 ± 11, 253.8 ± 1.7 and 235.7 ± 6.1 Ma [49], which indicates the multiphase introduction of melts. In addition, significant variations in εHf for different rocks of the Norilsk 1 intrusion suggest different sources that correspond to the parameters of varying degrees of interaction between the crust and the lithospheric mantle [49].
Vein-disseminated ores in the exocontact intrusion differ in their composition from overlying disseminated ores by the prevalence of pyrrhotite, and have higher contents of PGE: up to 10 ppm in borehole PH-222, and up to 20 ppm-in borehole PH-193 (Figure 3c,d). Therefore, these ores cannot be the result of the sedimentation of droplets at the bottom, as is assumed in the model. An alternative model suggests that the sulfide liquid was segregated from the silicate magma elsewhere and that this sulfide liquid was later injected between the consolidated intrusive and sedimentary rocks [50,51].

Conclusions
Thus, the following conclusions have been established on the basis of the mineralogical and geochemical features that:

1.
The Ni/Cu ratios are decrease in each stratigraphic layer of rocks, and from picritic toward olivine (or taxite) gabbro-dolerites as a whole, in agreement with the increase in chalcopyrite in this direction; 2.
The Ni/Fe ratios in pentlandite increase from top to bottom in each layer, and from picritic toward olivine (or taxite) gabbro-dolerites and to massive ores, which indicates an increase in sulfur fugacity in the mineral parageneses down the section of the borehole; 3.
There is a clear correlation between the sulfide assemblages and the type of the host gabbro-dolerites: picritic gabbro-dolerites are characterized by a low-sulfur and Cu-rich sulfide assemblage; olivine and taxite gabbro-dolerites are characterized by a high-sulfur assemblage of sulfides. The differences in the types of mineralization are due to the particular compositions of sulfide melts and the different physicochemical conditions of their fractionation; 4.
Taxite and picritic gabbro-dolerites cannot be fractionated from a single melt in the formation chamber, but are the result of a two-stage magma injection of various portions containing sulfide liquids of different compositions.

5.
Vein-disseminated ores in the contacts of intrusions are not the result of the deposition of sulfide droplets at the place of formation, but are due to their later injection.
Author Contributions: N.T. conceived and designed the study, interpreted the results, and wrote this article. G.S. prepared detailed descriptions of numerous ore samples. A.P. provided the chemical analyses of the rocks and edited the manuscript. V.K. provided the analyses of minerals made on the WDS spectrometer. All authors have read and agreed to the published version of the manuscript.

Funding:
This study was carried out within the framework of the state assignment of the VS Sobolev Institute of Geology and Mineralogy of the Siberian Branch of the Russian Academy of Sciences (financed by the Ministry of Science and Higher Education of the Russian Federation). We also acknowledge the financial assistance provided by the Novageo LLC, projects nos 10/17.