Layered mafic-ultramafic complex with an outcrop area of about 8 km2.
the Niubiziliang mafic-ultramafic complex displays discernible morphological features that facilitate its categorization into three distinct units, denoted as Nos. 1, 2, and 3, based on their respective shapes. The No. 1 complex presents as a horseshoe-shaped body with approximate dimensions of 300 m in length and 200–300 m in width. It occurs as a xenolith within the Devonian diorite intrusion and is predominantly composed of gabbroic lithologies.

The No. 2 complex exhibits a distinctive lens-like morphology, characterized by an elongated body measuring approximately 680 m in length and 20–250 m in width, dipping at an angle of approximately 68° towards the northwest, This complex is predominantly composed of lherzolite and olivine websterite (Ol-websterite), which are commonly found rocks in mafic-ultramafic complexes. At the surface, the southern part of the No. 2 complex is dominated by lherzolite, which consists of olivine (45%–65%), orthopyroxene (8%–20%), and clinopyroxene (10%–25%), with minor plagioclase and hornblende contents (Fig. 3a). In contrast, Ol-websterites are primarily found in the northern part of the No. 2 complex and have compositions of olivine (20%–40%), orthopyroxene (15%–30%), and clinopyroxene (15%–30%) (Fig. 3b). The olivine grains are euhedral and subhedral (Fig. 3c), with sizes ranging from 0.10 to 0.30 mm, and some grains are completely serpentinized, indicating alteration processes that have occurred in the complex. The No. 2 complex contains five distinct Ni ore bodies hosted in Ol-websterite, ranging in length from 40 to 160 m and with thicknesses varying from 1.62 to 22 m, These ore bodies exhibit average grades of 0.22% to 0.79% Cu, 0.20% to 1.57% Ni, and byproduct Co contents of 0.03% to 0.08%. The thickest ore body, located in the No. 2 complex, measures 41.1 m in thickness and displays an average Ni grade of 0.56%, with a maximum grade of 1.57% Ni. The No. 3 complex contains seven ore bodies dominated by Ni and Cu, with thicknesses ranging from 1.10 to 5.16 m, Ni grades ranging from 0.30% to 0.48%, and associated Cu and Co mineralization.


The No. 3 complex displays a distinctive wedged-like body morphology, spanning a length of 1000 m with a width ranging from 20 to 250 m. It is characterized by a dipping angle of approximately 47° towards the northwest–west direction. These rocks consist of lherzolite, plagioclase-bearing lherzolite (Pl-bearing lherzolite), Ol-websterite, and gabbro (Fig. 2). Upon close examination of the surface, it is evident that the southern and middle sections of the No. 3 complex are predominantly composed of lherzolite and Ol-websterite, respectively. The petrographic characteristics of these rock types closely resemble those observed in the No. 2 complex. In contrast, the northwestern part of the No. 3 complex is dominated by gabbro, which primarily consists of clinopyroxene (45%–60%), plagioclase (50%–55%), and minor amounts of amphibole (0%–5%) and quartz. The clinopyroxene in the gabbro is predominantly pyroxene, exhibiting a short columnar structure with an average particle size ranging from 0.20 to 0.30 mm. Notably, some particles exhibit evidence of amphibole and chlorite alteration at the edges, indicating past alteration processes within the complex.

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References