Characteristic of Specialized Geochemistry of the Ngoc Tu Granitoid Block KonTum, Vietnam

Abstract

The determination of magmatic mineralogy based on the oxidation-reduction state of magma by primary inclusion geochemistry of RAMAN equipment has identified Ngoc Tu granitoid blocks in the oxidation state represented by CO2-rich primary inclusions. Redox conditions help explain the specialized chemistry of geochemistry not only at the content level, but also in terms of the geochemical behavior of the elements. This shows that the Ngoc Tu granitoid block is not favorable for the metal potential of Sn, but is favorable for the movement of Mo and W from the magma solution to the ore solution.

1. Introduction

Ngoc Tu block granite in particular has been studied by many works and has conception related to tin (Sn), wolfram (W) mineralization potential. However, there has not been any work that clearly confirms the Sn mineral-forming ability in Ngoc Tu block, although Duong Duc Kiem [1] discovered Sn mineralized expression. This result is based on the geochemical parameters of the epigenetic zone, with the geochemical document of the primary rock using semi-quantitative methods, which has no meaning in determining the specialization of magma. At the same time, the types of changes related to mineralization have not been detailed.

Meanwhile, the geochemical specialization of molybdenum (Mo) has not been determined; Sn, W, Cu are determined by semi-quantitative method. In particular, the oxidation-reduction state of a granitoid has not been studied, and this is a decisive condition for the geochemical behavior of Sn, Mo, W, Cu, … capable of moving from the magma when bound.

To clarify this problem, surveyed and sampled (Figure 1) studied the system from the edge to the center of the mass, the facies of the granite, the variable zone, and related geological structure. Since then, building the quantitative database includes: (1) analysis of 24 samples of thin sliced granite (12 samples of porphyr granite, 6 samples of small grain granite, 13 samples of modified granite rocks); (2) analysis of 21 geochemical samples of rare elements; and (3) analysis of protozoa composition in total rock.

Figure 1.

Sampling location of Ngoc Tu granitoid block, KonTum, Vietnam (• Sampling point).

2. Geological characteristics of Ngoc Tu block

The Ngoc Tu granite block (Figure 2) is one of the highest mountain peaks in the region, about 16 km northwest of Dak To district, KonTum province. Previously, Ngoc Tu granite block was established by Tran Tinh, Nguyen Van Trang, (1994) [2], Nguyen Quang Loc (1998) [3] and classified into Ba Na complex with age K2. Ngoc Tu block has a fairly isometric shape, an area of about 120 km². This granite block penetrates the biotite gneiss, plagioclase of the Tac Po formation, and the biotite granite of the Hai Van complex. Albitization and horny rocks are common at the contact edge: quartz horn—feldspar—mica, quartz horn—biotite—cordierite. The lithological composition of the block consists of brightly colored granite but has many different facies and the boundary is not clear, including: porphyritic to medium-grain granitoid, and small-grain granitoid. In addition, there is a vascular phase in the internal magma block (Figure 3).

• Phase 1 has a medium, relatively light-colored granite granite type with block structure. Ingredients mainly include feldspar, quartz, muscovite, biotite.

Figure 2.

Location of Ngoc Tu granitoid block in the Central Highlands region, Vietnam.

Figure 3.

Image of granitoid porphyr and granitoid medium-small.

Mineral composition: The main minerals are plagioclase (40 ÷ 42%), potassium feldspar (orthoclass + microcline) 32 ÷ 34%, quartz 23 ÷ 25%, biotite 2%, muscovite from 1 ÷ 2%. Biotite is chlorinated.

• Phase 2 has a pattern of granite with small to medium grain, relatively dark color, with block structure. Ingredients mainly include feldspar, quartz, muscovite, and biotite.

Mineral composition: The main minerals are plagioclase (20 ÷ 31%), potassium feldspar (orthoclass + microcline) 34 ÷ 49%, quartz 26 ÷ 30%, biotite 1 ÷ 2%, muscovite 1 ÷ 2%. Biotite is often chlorinated.

• The berezitized change zone has the following characteristics: 1/The residual base rock is potassium feldspar (52 ÷ 53%) in a large slab form, very uneven distribution, opaque surface, along the open sand of potassium feldspar densely developed squamous sericite. 2/Hydrothermal part: very uneven distribution; the composition is quartz (35 ÷ 37%), distorted large grains, muscovite (3 ÷ 4%) in slabs, distorted, colorless, highly interfering; sericite (7 ÷ 9%) scaly, clean surface, often clumping—uneven drive.

The age of zircon formation in granitoid determined by U-Pb, zircon, SHRIMP method at AP Kapinski (VSEGEI) was 244.5 ± 1.5 million (T2) according to Nguyen Van Niem [4]. This result is similar to the determination of the isotopic age by U - Pb method for granite of Ba Na type in Ngoc Tu block for the age of 239 ÷ 240 million years, corresponding to T2 [5].

Tectonic faults: The northwest-southeast fault system has quite strongly divided, creating strong fracture zones, favorable for later hydrothermal processes.

3. Materials and methods

With the aim of clarifying the mineralogical role of the Ngoc Tu block granite formation, samples were collected for each rock type, zone of change, and mineralized expression zone, including lithological thin slices, basal geochemical samples and zone of change, and sample for study of the composition of primary magma.

The trace element geochemical samples were analyzed by ICP-MS method at the Far East Geological Institute-FEGI (Russia) systematically from the edge of the block to the center, characteristic of rock types including: a granite rich in pegmatite, medium grain granitoid, small grain granitoid, zone of change, zone of fracture tectonic, sulfide zone. This sample serves to study geochemical specialization, to determine minimum anomaly and mutation values that contribute to mineral search.

The protoplasmic specimen in magma is done in the following steps: Research and sampling ensure the representativeness of the sample for each rock type. Processing and analyzing two types of rocks including: small and medium grain biotite granite with transition boundary; small grain biotite rock in the tectonic break zone. Samples are processed to a thickness of about 1.0÷1.3 mm, polished, size 2.5×4.5 cm. The samples were processed and analyzed on Raman equipment at the Laboratory of Far East Geology (Russia). The protoplasmic holster is characterized by the following properties: It is contained in crystals and is part of a random connection; an indication of the direction of crystal growth can be observed if the capsule is large enough 1/10 times the crystals that contain them) or the form evolving in three directions (this is a very reliable sign); it can be in the center, edge, or crystal position of driftwood; in a crystal contains only 1 capsule; protozoa often have irregular, small (secondary or combined) envelopes arranged around or opposite.

The general analytical procedure is as follows: microscopy and protozoa detection, selection of suitable size capsule (> 1 pm, optimal 10 pm or more), marking position on slice, drawing preliminary shape—characteristics of the capsule; transfer to Raman device, prepare the device with sample C, put the sample of the specimen marked with the object into the analysis position, choose the full wavelength for scanning, separate each wavelength according to analytical composition, record and save data, and transfer it to the server system to process results. This method helps to study the primary inclusion composition of the aggregate rock, interpret the oxidation-reduction state of the granite most accurately, and evaluate the biochemistry of the granitoid. However, the microscopic rock type has not been able to detect the protozoa because the probability of detecting it in the rock is very low (about 10%) and their size is small (<1 pm). Only protozoa in rocks are used to study the oxidation-reduction state of magma.

In addition, the authors also collected, studied, and used the main components and traces of the rock to calculate the oxidation-reduction conditions. From there, compare with the primary holistic research method.

4. Results and discussion

4.1 Results of the analysis of the body

Fluid composition in primary inclusions of light-colored porphyry and medium-small-grained granites is analyzed by Raman instrument at the Institute of Far Eastern Geology, Sub-Institute of the Academy of Sciences of the Russian Federation

• Bright porphyr granite meets primary inclusions in quartz mineral background (Figure 4).

• Light porphyric granite transition from the first type rock (Figure 4) in this zone in the primary inclusion in quartz mineral.

• Light-colored medium-small-grained granite: This type of stone has a transition boundary.

Figure 4.

Variation of granitoid porphyr (II, III) and granitoid medium-small (III) in Ngoc Tu granitoid block.

In contact with light-colored porphyric granite, a primary inclusion was discovered.

The results of the analysis are as follows:

• Raman spectroscopy to determine the primary inclusion composition in CO₂-containing quartz minerals with a change in the granitoid from type 1 located in this zone, the primary inclusion in the quartz mineral containing CO₂ with density 0.23–0.35 g/cm³ from 1283.7 to 1387.0 cm⁻¹ to type 2, located in this rock type, distributed independently, far from the boundary of contact with metamorphic rocks as well. Primary inclusions are encountered in quartz minerals that exist with density 0.15–0.25 g/cm³ with a spectral range of CO₂ from 1285 to 1388.1 cm⁻¹ and type of 3 primary inclusion sites located at in quartz minerals exist with density 0.17–0.28 g/cm³ with the spectral range of CO₂ from 1353 cm⁻¹ (Figure 5).

• Raman spectroscopy determines the composition of primary inclusions in quartz minerals containing H₂O in liquid form of granitoid rock types, including: type 1 meets primary inclusions in the background of H₂O-containing quartz minerals with a spectral range of 3625 cm⁻¹ in gaseous state to type 2 meets primary inclusions in H₂O-containing quartz minerals, the spectral range is 3575 cm⁻¹ in liquid form, and type 3 meets primary inclusions in H₂O-containing quartz minerals with a spectral range of 3625 cm⁻¹ in liquid form (Figure 6).

• Spectral band of primary inclusion of fluorapatite (Ca₅(PO₄)3F surrounded by quartz crystals of granitoid rock types including: type 1 at the location where F—fluorapatite-rich primary inclusions (Ca₅(PO₄)3F) are encountered in quartz crystal has a spectral range: 464–963.2 cm⁻¹, type 2 at the location where F–fluorapatite-rich primary inclusions (Ca₅(PO₄)3F in quartz crystals are found) has a spectral range: 429–465–965 cm⁻¹ (Figure 7).

Figure 5.

Raman shift determines the primary inclusion composition in CO₂-containing quartz minerals of Ngoc Tu block granitoid types.

Figure 6.

Raman shift determines the primary inclusion composition in H₂O-containing quartz minerals of Ngoc Tu block granitoid types.

Figure 7.

Raman shift determines the primary inclusion composition in fluorapatite (Ca5(PO4)3F-containing quartz minerals of Ngoc Tu block granitoid types.

The above results show that, in Ngoc Tu block granitoid from the first rock type to the second and third type, there is an increase in the composition and concentration of fluid in the primary inclusion, specifically rich in CO₂ and H₂O, which is shown by the results, clearly oxidizing properties of rocks [6]. In addition, the appearance of F-rich inclusions is typical for the volatile composition and the small-medium-grained granite that was born after the expression of increased H₂O composition in the primary inclusion.

Thus, the research results on the magma environment show that the Ngoc Tu block granitoid has a moderate to strong oxidizing environment. This environment is typical for the mineralization of Mo, W, and U, which is not favorable for the formation of Sn deposits. Only two protoplasmic inclusions were found in a medium-grain biotite granitoid sample, which was contained in a quartz crystal.

4.2 Oxidation state of Ngoc Tu granitoid

Light-colored granite porphyr occupies the main area of Ngoc Tu mass. The analysis results show that the crystals in quartz crystals find CO₂ (Figure 3), which characterizes the primary, oxidizing magma environment.

Redox states are also expressed by the main components (Fe) and trace. However, these factors are very easy to be affected by the process of secondary transformation. Here, bright granite with Fe₂O₃/FeO > 0.5 ratio is typical for oxidized granitoid and vice versa, and bright granite with Fe₂O₃/FeO ratio < 0.5 is typical for reduced granitoid. For Ngoc Tu, according to the distribution and correlation characteristics between Fe²⁺ and Fe³⁺ [3], magma granitoid solids exhibiting moderate-to-strong oxidation (Figure 8) have favorable ability to generate W, W-Mo (Figure 9). However, the use of Fe²⁺ and Fe³⁺ to divide the geochemical environment of the jade granite magma also showed both oxidation and reduction (medium to strong) medium (Figure 8), which may be caused by granite rocks. This block is affected by chloritization, less muscovitization, and epidotization.

Figure 8.

Diagram of classification of oxidation-reduction conditions of Ngoc Tu block granite [7].

Figure 9.

Correlation diagram between oxidation conditions and differentiation level of Ngoc Tu granite in relation to mineralization [7].

4.3 The geochemical specialization of the jadeite block Ngoc Tu

For large granitoid porphyria, there is no localization of Mo (Ktt = 1.36) Sn, W, Pb, Th are specialized. U has medium specialization, while Re shows very high specialization (Table 1). This result for Mo is in contrast to previous studies, and the reliability of the data is more assured. However, W is only for reference because the analysis has a large random error, but the analytical results of this element still clearly distinguish from the reality between the bedrock-change zone and mineralization zone.

• For the granitoid of small particles, element Mo has high specialization (Ktt = 4.51) (Table 2), close to the high geochemical threshold. This result is determined for the first time by the same spatial and time relationship with the large-grained porphyritic granite and quartz-molybdenite ore circuits (the results of previous studies have not clarified this). The set of datasets are tested to ensure calculation. Other elements such as W have high geochemical specialization, U has a geochemistry specialization (Ktt = 6.07), Pb also has geochemical specialization, and Sn also exhibits geochemical specialization (Table 2) but is low than porphyr granite. Thus, Mo, U, W in small granitic granite have much higher specialized properties than large grain porphyritic granite.

NT	Min (ppm)	Max (ppm)	TB (ppm)	(S)	V (%)	Ktt	A	B
Li	16.17	117.98	59.88	30.27	50.54	0.75	80
Be	3.14	9.81	5.07	1.84	36.22	1.45	3.5
Sc	3.70	5.40	4.48	0.49	11.01	0.64	7
V	10.49	23.36	16.45	3.28	19.92	0.23	70
Cu	1.85	30.26	6.44	7.75	120.39	0.26	25
Zn	21.02	37.38	30.46	4.91	16.12	0.53	58
Ga	14.10	18.40	16.09	0.95	5.93	0.85	19
Ge	2.68	3.91	3.01	0.30	9.86	2.01	1.5
Rb	350.57	446.43	392.17	29.64	7.56	1.96		200
Sr	38.01	76.04	58.39	11.48	19.67	0.22	270
Y	17.88	56.49	27.37	10.42	38.07	0.68	40
Nb	13.29	19.88	15.77	1.83	11.61	0.79	20
Mo	0.45	9.41	2.04	2.69	131.63	1.36	1.5	1
Cd	0.03	0.09	0.05	0.01	30.72	0.27	0.17
Sn	5.15	10.81	7.30	1.54	21.06	2.43	3
Cs	11.62	32.78	20.33	6.33	31.13	4.07		5
Ba	200.54	538.59	328.30	84.62	25.77	0.47	700
Hf	2.44	4.40	3.56	0.61	17.17	3.56		1
Ta	1.63	3.61	2.55	0.66	25.83	1.02	2.5
W	0.90	44.50	6.57	10.63	161.69	3.29	2
Re	0.00	0.02	0.01	0.00	33.79	18.78	0.00067	Re
Pb	35.40	48.51	43.97	3.63	8.25	2.20	20
Th	27.93	52.35	38.35	6.97	18.18	2.13		18
U	4.44	32.52	12.35	7.79	63.02	3.53		3.5

Table 1.

The geochemical parameters of the Ngoc Tu block porphyritic granitoid (n = 12 samples).

NT	Min (ppm)	Max (ppm)	TB (ppm)	(S)	V (%)	Ktt	A	B
Li	22.09	35.03	27.87	5.34	19.16	0.35	80
Be	3.03	13.32	7.42	4.40	59.35	2.12	3.5
Cu	5.98	28.10	20.15	10.28	50.99	0.81	25
Zn	8.53	15.92	12.76	3.08	24.14	0.22	58
Ga	13.64	19.81	15.66	2.82	17.99	0.82	19
Ge	2.10	2.37	2.21	0.12	5.40	1.48	1.5
Rb	399.28	442.14	418.95	17.62	4.21	2.09		200
Sr	16.51	38.45	28.08	9.20	32.77	0.10	270
Y	8.67	18.51	14.82	4.48	30.23	0.37	40
Zr	26.22	53.33	36.46	11.75	32.22	0.18		200
Nb	8.75	15.72	12.42	3.11	25.00	0.62	20
Mo	2.84	11.10	6.76	4.35	64.34	4.51	1.5
Cd	0.03	0.03	0.03	0.00	11.63	0.17	0.17
Sn	4.46	8.17	5.89	1.69	28.67	1.96	3
Ba	29.26	68.83	56.33	18.23	32.36	0.08	700
Hf	1.28	1.71	1.44	0.19	13.43	1.44		1
Ta	1.27	3.98	2.32	1.19	51.43	0.93	2.5
W	2.76	15.78	9.27	5.69	61.43	4.63	2
Re	0.00	0.01	0.01	0.00	40.42	13.22	0.00067	Re
Pb	37.42	59.31	49.22	9.98	20.28	2.46	20
Th	9.35	13.51	11.38	1.76	15.43	0.63		18
U	10.79	29.36	21.23	8.42	39.65	6.07		3.5

Table 2.

The geochemical parameters of the Ngoc Tu small grain granitoid (n = 6 samples).

Note: Value of clark of elements in granite: A— according to A.A. Golovin (2000); B—according to A. P. Vinogradov (1962).

4.4 Discussion

There are some differences in petrographic characteristics with previous research results: porphyr granite. Small grain granite is rare. The common bedrock change phenomenon includes: chlorination, albitization, epidotization, bezeritization; greisen turned. These characteristics form a solid basis for the interpretation of geochemical parameters and geochemical behavior of elements when determining localization.

The results on the protozoa composition characteristic for Ngoc Tu block-shaped granite magma medium have oxidation-reduction properties. Thus, in the evolutionary process of Ngoc Tu block magma from porphyritic granite with small granites increasing the composition and concentration of fluid in the primitive, rich in CO₂, H₂O clearly shows oxidation [6, 8] of granite study area, in which the sample did not detect any type of fluid. In addition, the appearance of F-rich capsules characterizes the volatile composition. Postpartum granitoid showed an increase in H₂O content in protozoa.

In addition to the primary mitochondria, there are also mixed and secondary mitochondria. Banded distribution characteristics, according to cracks or cracked protoplasm forming a foam form of small particles, indicate that the area is deformed. This phenomenon is probably also consistent with the process of cutting through the ancient metamorphic formations in the area that changes the specific pressure of the steam within the contact range, forming cracks in the internal mass and the redistribution of material components, including Mo.

The average arithmetic average content of Mo in Ngoc Tu mass is very high (135.94 ppm). Meanwhile, the weighted average content typical for Ngoc Tu block granite is 1.52 ppm (this value is usually lower than the value of the local background content). This very large difference between the arithmetic mean and this weighted mean reflects the very difference between the minimum negative anomaly (0.45 ppm) and the maximum content-max (3134.34 ppm) of sample set (18 samples) (Table 3, Figure 10). At the same time, this maximum value and some high content points (189.3 ppm) belonging to the max outlier sample were very significant for the search. Here, these two points (they are next to each other) have found quartz-molybdenum ores and sulfides of Cu, … Along with these two Mo mutant samples are also two points with mutation in Cu content and W. At the same time, at the variable zone near the quartz-molybdenite ore circuit, the mineral uraninite was found but the U content was not high (<10 ppm).

• The minimum anomaly value of Mo is 12.33 ppm. Above this threshold of content, there is an anomaly of 14.27 ppm, this point belongs to the bezeritized zone, containing several molybdenite particles in the region containing quartz-molybdenite small vessels (large particles, rose form) and many agar microchips. he covers an area of several hundred meters.

• The coefficient of variation of Mo content is very high (V = 460.32%) and the anomalous contrast of Mo is very large (254.21 ppm). This is possible, the mobility of Mo from the bedrock to the environment with favorable geological conditions will accumulate and create minerals. W, Cu also have high coefficient of variation, but the contrast of anomaly is much lower than Mo (Table 3). The distribution characteristics of Mo (Figure 11) are very different in small granites and large grain porphyrites. Meanwhile, in the porphyritic granite zone, it contains trans-shear quartz-molybdenite veins (Figure 12).

Parameter/element	Unit	W	Cu	Sn	Mo	Pb	Zn	U
No. of samples		18	18	18	18	18	18	18
% value of mutation	%	11.54	7.69	7.69	7.69	11.54	3.85	0.00
Standard deviation		296.86	114.42	6.90	625.78	27.94	13.52	296.86
Variation coefficient (V)	%	333.53	277.11	79.16	460.32	49.84	51.42	62.38
Min	ppm	0.90	1.85	1.41	0.45	35.40	7.13	1.38
Max		1445.90	501.04	35.04	3134.31	169.78	72.13	32.52
Median		5.63	5.37	6.90	1.52	46.22	27.44	10.79
Trung bình		89.01	41.29	8.71	135.94	56.06	26.30	13.08
Minimal positive anomaly		21.00	40.20	12.81	12.33	71.35	60.04	32.52
Minimal negative anomaly		0.90	1.85	1.47	0.45	35.40	7.13	1.38
Number of mutation values		2	2	0	2	0	0	0
Number of values above the minimum positive anomaly threshold		3	2	1	2	3	1	0
Number of values below the minimum negative anomaly threshold		0	0	1	0	0	0	0
Maximum value of mutation	ppm	1445.90	501.04	35.04	3134.31	169.78	72.13
Minimum value of mutation				1.41
Contrast of anomaly		68.85	12.46	2.73	254.21	2.38	1.20

Table 3.

The geochemical parameters of Mo and related elements of Ngoc Tu granitoid.

Notes: Minimum positive anomaly is a value indicating the ability to be related to the accumulation of an element that can form minerals. Minimum negative anomaly is a value that represents the possibility that it is involved in the abnormal movement of an element, which can lead to ore formation in a different location favorable in terms of geographic conditions.

Figure 10.

Diagram of determining the geochemical parameters (minimum anomaly, weighted average, mutation value …) of Ngoc Tu granitoid (Note: the max outlier on the chart is the value maximum, which can be equal to the spike value).

Figure 11.

Small particle molybdenite disseminated in Ngoc Tu granitoid microscopic fissure, sericiteized, less muscovitized, albitized.

Figure 12.

Molybdenite dissemination in modified rock bed in Ngoc Tu granite. Nicol (−), 100×.

Regarding the correlation characteristics between Mo and elements: Mo is an element that has no relationship (positively correlated) with any element in the Ngoc Tu block granite. At the same time, it is inversely correlated with the rare earth element group (REE), Sn, Zn, Ta, Hf, Th.

5. Conclusion

The properties of Ngoc Thu mass granitoid expressing both oxidation-reduction media based on the study of crystals in quartz crystals find CO₂ and the redox-redox state with main components (Fe) favorable for the mineralization of Mo, Cu–Mo, and W. Ngoc Tu block granitoid with high Re, Mo, W, U specialization, no mineralization of Sn. On the basis of the geochemical specialization Mo is quite suitable for accumulation such as the mineralization point Mo, W.