**Summary of Pre-Accretionary and Accretionary Metallogenic Belts of
Mongolia**

**By Gunchin Dejidmaa and Gombosuren Badarch**

**(Institute of Geology and Mineral Resources, Mongolian Academy of
Sciences, Ulaanbaatar, Mongolia)**

# INTRODUCTION

This report summarizes the major pre-accretionary and accretionary
metallogenic belts of Mongolia. This study will be expanded in future
years of the project. The major pre-accretionary and accretionary
metallogenic belts of Mongolia are plotted on, and interpreted according
to a preliminary schematic terrane map of Mongolia compiled at scale
1:10,000,000 by G. Badarch and O. Tomurtogoo in 1997 (Figure1).

The major pre-accretionary and accretionary metallogenic belts herein
summarized contain well-preserved deposits or occurrences of significant
size. Numerous, small pre-accretionary occurrence exist in Mongolia, but
cannot be displayed on Figures 2 and 3 at a scale of 1:10,000,000.
Preliminary data on the mineral deposits and occurrences of Mongolia are
summarized in the companion article by Deijidma and others (this
volume). These data are derived from the following sources:

> Guide to the geology and mineral resources of Mongolia, 1996,
> Jargalsaihan, D., Kazmer, M., Bara, Z., and Sanjaadorj, D., eds.:
> Geological Exploration Consulting Services (GCS) Co., 330 p., 2
> sheets, scale 1:3, 200,00.
>
> State Geological Fund, May 1997, Location map of base metal (Cu)
> deposits and occurrences of Mongolia, Series 2, 1 sheet, scale
> 1:3,200,000.
>
> State Geological Fund, May 1997, Location map of base metal (Pb, Zn,
> Ni, Co, Al) deposits and occurrences of Mongolia, Series 4, 1 sheet,
> scale 1:3,200,000.
>
> State Geological Fund, May 1997, Location map of industrial metal (Pb,
> Zn, Ni, Co, Al) deposits and occurrences of Mongolia, Series 3, 1
> sheet, scale 1:3,200,000.
>
> State Geological Fund, 1995, D. Largalsayhan, ed., Gold resources map
> of Mongolia, Series 5, 1 sheet, scale 1:3,200,000.

In future publications for the project, the compilation and synthesis of
the metallogenic belts of Mongolia and their contained significant and
major mineral deposits will be expanded. An article on gold metallogeny
of Mongolia that is related to this article was published by Dejidmaa
(1996).

# 

# PRE-ACCRETIONARY METALLOGENIC BELTS

Pre-accretionary metallogenic belts are interpreted as forming early in
the history of terranes, before accretion to other terranes or to a
continental margin. This type of metallogenic belts and contained
mineral deposits and occurrences are unique to the host terranes.
Typical examples of pre-accretionary metallogenic belts of Mongolia are
those related to ancient island arcs, continental margin arcs, and
passive continental margins and their derived terranes. For example, the
Nuuryn metallogenic belt is related to (hosted in) an ancient island arc
terrane. The Bayangol and southern Mongolian metallogenic belts are
related to a continental margin igneous arc terrane. And the Khovsgol
metallogenic belt is related to a passive continental margin terrane.
The major pre-accretionary metallogenic belts of Mongolia are depicted
in Figure 2, and the major characteristics of these belts are summarized
in Table 1.

## Pre-Accretionary Metallogenic belts Related to Island Arc Terranes

Metallogenic belts formed in ancient island arc terranes contain
relatively more deposit types compared to terranes of other tectonic
environments. For example, six deposit types are defined for the Nuuryn
metallogenic belt (Figure 2, Table 1). (1) Deposit types related to
ultramafic rocks (podiform Cr, serpentine hosted asbestos and
talc-carbonate) and mafic rocks (gabbroic Ni-Cu and gabbroic
Ti-magnetite). (2) Deposit types related to marine felsic to mafic rocks
(Cu-Zn massive and stringer deposits that are often rich in Au and Ag).
(3) Deposit types in chemical-carbonate rocks such as ironstone. (4)
Au-sulphide-quartz veins and stockworks associated with disseminated Au,
Au-Cu and Au-Cu-Fe skarns; (5) scheelite-quartz-stockwork greisen
deposits associated with calc-alkaline granitic intrusions. And (6)
deposit types related to intrusive porphyries (porphyry Cu-Au).

## Pre-Accretionary Metallogenic belts Related to Passive Continental Margin Terranes

Metallogenic belts formed in passive continental margin terranes or
overlap assemblages contain mostly deposits formed in carbonate and
sedimentary rocks and consist of phosphorite, bauxite, and ironstone
deposits and occurrences (Figure 2, Table 1).

## 

## Pre-Accretionary Metallogenic belts Related to Continental Margin Igneous Arc Terranes

Examples of pre-accretionary metallogenic belts formed in continental
margin igneous arcs are the Bayangol and the South Mongolian belts that
contain different deposit types (Figure 2, Table 1). This difference may
be to related to different levels of erosion of these belts and host
terranes. For example, the Bayangol belt, related to calc-alkaline
granitic intrusions, contains widespread Fe skarn deposits and lesser
Cu-Au and Cu skarn deposits. In contrast, the South Mongolian
metallogenic belt contains abundant porphyry Au-Cu deposits and related
deposit types, including high-sulphide epithermal Au, replacement
alunite, replacement kaolinite, and replacement pyrophylite deposits and
occurrences (Figure 2 and Table 1.).

# 

# ACCRETIONARY METALLOGENIC BELTS

Accretionary metallogenic belts are defined according to the following
features: (1) Occurrence in accretionary wedge terranes as interpreted
by G. Badarch (Figure1). The hosting accretionary wedge terranes all
contain mildly to intensively deformed and metamorphosed complexes of
turbidite formations and lesser amounts of oceanic rocks, mostly
ultramafic intrusive rocks. And (2) occurrence of specific deposit types
that are characteristic of accretionary or collisional tectonic
settings. A type example is Au-quartz vein deposit type that is clearly
structurally controlled, is hosted in deformed and metamorphosed
terrigenous formations, and has a close spatial relation and probably
genetic relation to synorogenic calc-alkaline granitic plutons. The
major accretionary metallogenic belts defined in this study are the
North Khentii, South Khentii, Bayangol, Khovd, Bayangobi, Olziit,
Nukhniinnuruu, Nemeegt-Gurvansaikhan, and Khatansuudal belts (Figure 3,
Table 2).

Accretionary metallogenic belts contain unique deposit types (Table 2).
The main deposit types are Au-quartz and Au-carbonate-quartz concordant
vein deposits (Figure 3, Table 2). These two types have clearly-defined
structural control and exhibit a close space and genetic relationship to
calc-alkaline gabbro to granodiorite intrusions. These deposits
generally occur in parallel veins, saddle reef veins, and networks of
veins that are always concordant with host terrigenous rocks. In many
cases, the distribution of the veins is controlled by anticlinal axes,
shear zones, and a greenschist facies metamorphic grade.

A second, lesser deposit type in accretionary metallogenic belts is
possibly ironstone or iron-manganese-stone deposit (Figure 3, Table 2).
These deposits types are widespread in Mongolia.

The third, lesser deposit type in accretionary metallogenic belts is
Cu-Ag-quartz vein or linear stockwork (Figure 3, Table 2). The type is
widely distributed in the Khovd metallogenic belt, especially in the
Ordovician-Silurian Biji unit.

# 

# REFERENCES CITED

Dejidmaa, G., 1996, Gold metallogeny of Mongolia, Mongolian
Geoscientist, no. 1, p. 6-29.

Dejidmaa, G., Chimed, L., and Badarch, G., 1998, Preliminary table of
lode and placer deposits and occurrences of Mongolia, this volume.

Guide to the geology and mineral resources of Mongolia, 1996,
Jargalsaihan, D., Kazmer, M., Bara, Z., and Sanjaadorj, D., eds.:
Geological Exploration Consulting Services (GCS) Co., 330 p., 2 sheets,
scale 1:3, 200,00.

State Geological Fund, May 1997, Location map of base metal (Cu)
deposits and occurrences of Mongolia, Series 2, 1 sheet, scale
1:3,200,000.

State Geological Fund, May 1997, Location map of base metal (Pb, Zn, Ni,
Co, Al) deposits and occurrences of Mongolia, Series 4, 1 sheet, scale
1:3,200,000.

State Geological Fund, May 1997, Location map of industrial metal (Pb,
Zn, Ni, Co, Al) deposits and occurrences of Mongolia, Series 3, 1 sheet,
scale 1:3,200,000.

State Geological Fund, 1995, D. Largalsayhan, ed., Gold resources map of
Mongolia, Series 5, 1 sheet, scale 1:3,200,000.

# TITLES TO FIGURES

Figure 1. Schematic terrane and overlap assemblage map of Mongolia.
Compiled by G. Badarch and O. Tomurtogoo, 1997.

2\. Major pre-accretionary metallogenic belts and associated mineral
deposits, and occurrences of Mongolia.

3\. Major accretionary metallogenic belts and associated mineral
deposits, and occurrences of Mongolia.

# Table 1. Pre-accretionary metallogenic belts and associated mineral deposits, and occurrences of Mongolia

  --------- ---------------- ---------------- ------------------ ----------------------- --------------
  **No.**   **Metallogenic   **Host terrane   **Host Rocks**     **Deposit type**        **Examples**
            belt**           (Tectonic                                                   
                             Environment)**                                              

  1         Nuur             Nuur (Early      Deposits related   Cyprus Cu - Zn - Ag (   Borts Uul
                             Paleozoic island to marine mafic to Au ) massive and        deposit,
                             arc)             felsic extrusive   stringer-impregnation   Gozgor and
                                              rocks              sulfide                 Narandavaa
                                                                                         occurrences
                                                                                         and others.

                                              Deposits in        Iron formation          Bayan Airag
                                              carbonate and                              Uul, Hulj gol
                                              chemical -                                 occurrences
                                              sedimentary rocks                          

                                              Deposits related   Au--sulfide quartz vein Hyargas, Budag
                                              to calc - alkaline and stockwork           Hond,
                                              granite intrusive  associated with         Tsetserleg
                                                                 disseminated Au         Nuruu
                                                                                         occurrences

                                                                 Au-Cu skarn             Togloy
                                                                                         occurrence

                                                                 W (scheelite) greisen   Morit Uul
                                                                                         occurrence

                                              Porphyry pluton    Porphyry Au-Cu          Beger group
                                              hosted deposits                            occurrence

                                              Deposits related   PGE-rich podiform Cr    Hantaishir
                                              to mafic and                               group
                                              ultramafic rocks                           

                                                                 Serpentinite-hosted     Hyargas
                                                                 asbestos                occurrence

                                                                 Talc-carbonate          Hyargas, Hotol
                                                                                         occurrences

                                                                 Gabbroic Ni-Cu,         Jargalant and
                                                                 gabbroic Ti -Fe         Uet Ondor
                                                                                         occurrences

  2         Bayangol         Bayangol terrane Deposits related   Au-Cu-Fe skarn, Cu      Oyut Tolgoy
                             (Early Paleozoic to calc-alkaline   skarn, Fe skarn         and Daagandel
                             continental      granite intrusives                         occurrences;
                             margin arc)                                                 Tomortey,
                                                                                         Bayangol,
                                                                                         Tomortolgoy
                                                                                         deposits

                                              Deposits related   Asbestos skarn          Baishin hudag
                                              to                                         
                                              mafic-ultramafic                           
                                              intrusives                                 

                                                                 Gabbroic PGE rich Cu -  Nomgon , Hotol
                                                                 Ni                      occurrence
  --------- ---------------- ---------------- ------------------ ----------------------- --------------

  --- ----------- ------------------- --------------- ------------------- -------------------------------- -------------
  3   South       Middle-upper        Porphyry and                        Porphyry Au-Cu                   Kharmagtai,
      Mongolian   Paleozoic           granitic                                                             Uhaa Hudag,
                  continental margin  pluton-hosted                                                        Ovoothyar
                  arc                 deposits                                                             occurrences

                                                                          High-sulfide epithermal Au       Shuteen, Ikh
                                                                                                           Shanhai
                                                                                                           occurrences

                                                                          Au-sulfide-(tourmaline)-quartz   Ovoothyar,
                                                                          vein or stockwork                Shine
                                                                                                           occurrences

                                                      Au-sulfide-                                          Ovoothyar,
                                                      tourmaline-quartz                                    Kharmagtai
                                                      breccia zone/                                        occurrences
                                                      explosive pipe                                       

                                                      Alunite replacement                                  Shuteen, Ikh
                                                                                                           Shanhai
                                                                                                           occurrences

                                                      Kaolinite                                            Shuteen, Ikh
                                                      replacement                                          Shanhai
                                                                                                           occurrences

                                                      Prophyllite                                          Tsogt Tsetsiy
                                                      replacement                                          Group
                                                                                                           occurences

  4   Hovsgol     Lower Paleozoic     Carbonate and   Phosphorite                                          Urandosh,
                  passive continental chemical                                                             Jankhai,
                  margin or           sedimentary                                                          Mankhan Uul,
                  post-accretionary   rocks                                                                Burenhaan
                  overlap assemblages                                                                      deposits

                                                      Ironstone bauxite                                    Khachim Gol,
                                                                                                           Sayhangol
                                                                                                           occurrences

  5   Tsagaan                                         Phosphorite                                          Tsagaan Olom
      Olom                                                                                                 group
                                                                                                           occurrences
  --- ----------- ------------------- --------------- ------------------- -------------------------------- -------------

### Table 2. Accretionary metallogenic belts and associated mineral deposits, and occurrences of Mongolia

  --------- ----------------- -------------- ---------------------- --------------------- --------------
  **No.**   **Metallogenic    **Host         **Host Rocks**         **Deposit Type**      **Examples**
            Belt**            Terrane**                                                   

  1         North Hentey      Zag terrane    Deposits in            Ironstone             Eroo gol
                              (Early         chemical-sedimentary                         group, Huj
                              Paleozoic      rocks                                        gol, Buugert
                              accretionary                                                group
                              wedge)                                                      

                                             Deposits related to    Cu-Ag vein and linear 
                                             regionally             stockwork             
                                             metamorphosed rocks                          

                                             Deposits related to    Au quartz vein        Bumbat, Nariyn
                                             calc-alkaline granite  (anticline axis       gol deposits,
                                             intrusive              control)              Zaamar group
                                                                                          occurrences

  2         South Hentey      Zag terrane    Deposits in            Ironstone             Navchit gol,
                              (Early         chemical-sedimentary                         Oborhondlon,
                              Paleozoic      rocks                                        Delger Ondor,
                              accretionary                                                and Berh Uul,
                              wedge)                                                      occurrences

                                             Deposits related to    Au-quartz vein        Balj gol and
                                             regionally                                   Baruun muhar
                                             metamorphosed rocks                          groups
                                             and calc-alkaline                            
                                             granite intrusive                            

  3         Bayanhon-Hongor   Bayanhongor    Deposits related to    Au - quartz vein,     Burd gol, Han
                              terrane        regionally             Au-carbonate-quartz   Uul, Dovont
                              (Precambrian   metamorphosed rocks    vein                  occurrences
                              to middle      and calc-alkaline                            (Bayanhongor
                              Paleozoic      granite intrusives                           area)
                              accretionary                                                
                              wedge)                                                      

  4         Hovd              Hovd terrane   Deposits related to    Au quartz vein        Altantsogts,
                              (Lower to      regionally                                   Hovd
                              middle         metamorphosed rocks                          occurrences in
                              Paleozoic      and calc - alkaline                          Shar hooloy
                              accretionary   granite intrusive                            district
                              wedge)                                                      

                                                                    Cu-Ag quartz linear   Bij group
                                                                    stockwork             occurrence in
                                                                                          Manhan area

                                             Deposits in chemical - Ironstone             Uureg nuur
                                             sedimentary rocks                            group

  5         Bayangovi         Gobi Altai     Deposits related to    Au - (carbonate)      Bayangovi
                              terrane (Lower regionally             quartz vein (saddle   group, Oortsog
                              to middle      metamorphosed rocks    reef veins and        and Bituugiyn
                              Paleozoic      and calc-alkaline      stockwork in          hyar
                              accretionary   granite intrusive      sandstone)            occurrences
                              wedge)                                                      

                                                                    Cu - Ag quartz vein   Bayangovi
                                                                    and linear stockwork  group
                                                                                          occurrence

  6         Olziyt            Gobi-Altai     Deposits related to    Au - (carbonate)      Olon Ovoot and
                              terrane (Lower regionally             quartz vein (saddle   Antsavyn,
                              middle         metamorphosed rocks    reef veins)           Dayangar
                              Paleozoic      and calc-alkaline                            occurrences
                              accretionary   granite intrusives                           
                              wedge)                                                      
  --------- ----------------- -------------- ---------------------- --------------------- --------------

  --- ---------------------- --------------- ------------------ --------------- -------------
  7   Nuhniy Nuruu           Baytag terrane  Deposits related   Au -            Haltar Uul -
                             (Middle         to regionally      (carbonate) -   Ereen uul
                             Paleozoic       metamorphosed      quartz vein     group
                             accretionary    rocks and          (saddle reef    occurrences
                             wedge)          calc-alkaline      veins)          
                                             granite intrusives                 

                                             Deposits in        Ironstone       Suultolgoi
                                             chemical -                         occurrence
                                             sedimentary rocks                  

  8   Nemegt-Gurvan-Sayhan   Zoolon and      Deposits related   Au (carbonate)  Nemegt
                             Gurvan-sayhan   to regionally      quartz vein     occurrence
                             terranes (Early metamorphosed                      
                             and middle      rocks and                          
                             Paleozoic       calc-alkaline                      
                             accretionary    granite intrusives                 
                             wedge)                                             

  9   Hatansuudal            Naransevestey   Deposits related   Au (carbonate)  Talyn Meltes
                             terrane (Lower  to regionally      quartz vein     and
                             middle          metamorphosed      (parallel and   Hatansuudal
                             Paleozoic       rocks and          ladder veins)   occurrences
                             accretionary    calc-alkaline                      
                             wedge)          granite intrusives                 
  --- ---------------------- --------------- ------------------ --------------- -------------