Full text of DOI:10.1007/BF02959444

Vol. 43 No. 4
SCIENCE IN CHINA (Series D)
August 2000
Strontium isotope geochemistry of the Lemachang
independent silver ore deposit, northeastern Yunnan, China
DENG Hailin (Ԍںॾ)1, LI Chaoyang (हдཽ)1, TU Guangzhi (ැڛѨ)1,
ZHOU Yunman (ᄻၩਁ)2 & WANG Chongwu (ฆѬ๓)2
1. The Open Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences,
Guiyang 550002, China;
2. No. 1 Geological Party of the Yunnan Bureau of Geology and Mineral Resources, Xundian 655205, China
Correspondence should be addressed to Deng Hailin (email: hldeng@public1.gy.gz.cn)
Received January 8, 1999
Abstract Sr isotope geochemical studies (the 87Sr/86Sr and ꢀ18O-87Sr/86Sr systems) on the wall
rocks and ores from the Lemachang independent Ag deposit in northeastern Yunnan provide
strong evidence that the ore-forming fluids had flown through radiogenetically Sr-enriched rocks or
strata prior to their entry into the locus of ore precipitation, and water-rock interaction is the main
mechanism of Ag ore precipitation. The radiogenetically Sr-enriched source region may be the
Proterozoic basement (the Kunyang and Hekou groups). Moreover, the theoretical modeling of the
Sr isotopic system indicates that the ore-forming fluids contain as much as 3×10ꢁ6 Sr with isotopic
composition of Sr being 0.750 and that of oxygen 7.0‰. The ore-forming temperatures were
estimated at 150ü250ć for the carbonate rock-type ores and at 200ü260ć for the clastic
rock-type.
Keywords: Lemachang, northeastern Yunnan, independent Ag deposit, Sr isotope, ore-forming fluid.
From the late1980s to the early 1990s a new type of independent Ag deposit was discovered
and represented by the Lemachang large (or super-large) independent Ag ore deposit in the
Mississippi valley-type Pb-Zn ore belt in northeastern Yunnan. Nevertheless, no systematic work
has been done in this aspect. The so-called independent Ag deposits are chemically predominated
by Ag, which are significantly different from those associated or coexisting Ag deposits.
Independent Ag deposits can be exploited and utilized independently and they were formed under
unique geological conditions. Since the 1970s Ag has become one of the most urgent mineral
resources in China. Exploration of and research on independent Ag deposits and super-large
independent Ag deposits can effectively and rapidly release the contradiction between its supply
and demand. On the other hand, (i) research on independent Ag deposits can shed light on the
geochemical properties of Ag in them, and also is an important approach to filling the gap in this
aspect; (ii) Ag deposits, especially independent Ag deposits, are usually formed in the moderate to
low ranges of temperatures (100ü250ć), which is of great significance in exploring the
mechanism of low-temperature deposition of Ag and its low-temperature geochemical behavior
and enriching the theory of low-temperature geochemistry[1]. Sr isotopic research is a powerful
tool for investigating the source of ore-forming materials, the evolution path of ore-forming fluids

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ü
and the mechanism of ore deposition [2 4]. Systematic Sr isotope geochemical studies can provide
insight into the mechanism of metallogenesis of independent Ag deposits.
1
Geology
The Lemachang independent Ag deposit is located within the bounds of Ludian County,
northeastern Yunnan and geotectonically it lies in the Lemachang broken anticline in the northeast
Yunnan folded zone on the eastern side of the Xiaojiang fault in the western part of the Yangtze
Block1). The strata exposed in the mining district are the Lower Cambrian-Upper Permian
Emeishan basalts which are measured at 1 500 m in thickness. Due to the influence of the
Caledonian movement, all the strata are absent between the Middle-Upper Ordovician and the
Upper Carboniferous series with the exception of the Middle Devonian Qujing Formation
dolomites of small thickness (D2q)2). The Lemachang deposit occurs in the layered broken zone
of the NNE-extending Lemachang overthrust structure and the ores are largely stratiform and
stratoid in shape. As the overthrust structure cuts through the strata of various lithological
characters, significant differences are observed in both alteration and mineralization types in the
wall rocks of different lithological characters. In the carbonate strata (D2q dolomite and P1q+m
limestone) Ag-Pb mineralization dominates with dolomitization being the main alteration. And in
the clastic rock strata (Cambrian and Ordovician siltstones and sandstones) Ag-Cu mineralization
dominates with silicification and baritization being the main alterations. Dolomitization dominates
in the transitional zone between the above-mentioned two mineralization zones. Fluid inclusion
studies of dolomite and barite indicate that the temperatures of Ag-Pb mineralization are within
the range of 150ü200ć while those of Ag-Cu, 200ü250ć3). As deduced from the geology data,
the mineralization occurred during the Yenshanian period.
2
Samples and analytical methods
As the orebodies of commercial importance are hosted largely in carbonate rocks (mainly
dolomites), the carbonate-type ore samples were chiefly collected. Dolomite and barite
monominerals were hand-picked under binoculars, with a purity over 98%. The analytical
methods of samples are described below and the analytical results are presented in table 1. (i)
Rb-Sr isotopic analysis: Except that the barite samples were decomposed by the NaCO3
alkali-fusion method, the other samples were decomposed by acids. The separation and
concentration of Rb and Sr were effected on the cation exchange resin column, and the Rb and Sr
isotopic ratios were measured on a VG354 solid mass spectrometer. For the mass
1) The No. 1 Geological Party of the Yunnan Bureau of Geology and Mineral Resources, A regional report (scale: 1ĩ50000) on
the geology of Longtoushan-Jiemai area, Ludian County, Yunnan, P. R., China.
2) The No. 1 Geological Party of the Yunnan Bureau of Geology and Mineral Resources, A detailed regional report on the
exploration region of the Laojunshan mining section of the Lemachang Ag deposit, Ludian County, Yunnan, 1993.
3) Deng Hailin, Ore-forming geochemistry of the Lemachang single silver deposit, northeastern Yunnan Province of China with
special reference to fluid-rock interactions, Ph. D. Thesis of the Institute of Geochemistry, Chinese Academy of Sciences, 1998.

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339
spectrometrically analytical procedure, please refer to Liu Haichen et al.[5]. The 87Sr/86Sr ratios
were standardized in terms of 87Sr/86Sr=0.119 4; the international standard NBS987 yielded a
value of 0.710 346f15; the errors involved in Rb and Sr analysis <1%; and the errors involved in
87Sr/86Sr ratios <1%. Except for four samples which were analyzed at the Laboratory of Isotopes,
Institute of Geology, Chinese Academy of Sciences, the other samples were analyzed for their
Rb-Sr isotopes at the Laboratory of Radioactive Isotopes for Youth, Guangzhou Institute of
Geochemistry, Chinese Academy of Sciences. (ii) Oxygen isotopic analysis: The oxygen isotopic
analysis of carbonate rock and dolomite samples were conducted using the 100% phosphorus acid
method while that of siliceous rock and siltstone, the BrF5 method. The conversed CO2 gas was
analyzed on a MAT 251 EM mass spectrometer with SMOW as the standard with the analytical
precision being ꢂ0.2%. In the calculation of ꢀ18OSMOW[6], the following formula will be taken:
ꢀ 18OSMOW =1.030 86ꢃꢄꢀ 18OPDB+30.86. Oxygen isotopic analysis of all the samples was conducted
at the Laboratory of Stable Isotopes, Institute of Mineral Deposit Geology, Chinese Academy of
Geological Sciences.
Table 1 The O and Rb-Sr isotopic composition of rocks and ores in the Lemachang
independent Ag deposit, northeastern Yunnan
87Sr/86Sr
ꢀ18OSMOW
No. Sample No.
Sample description
Rb×10-6 Sr×10-6
Rb/Sr 87Rb/86Sr
87Sr/86Sr
(190 Ma)
(‰)
1
2
3
4
5
LMG-9
P1m+q limestone
D2q dolomite
28.2
0.087
4.841
36.98
12.40
10.45
185.6
99.56
102.2
71.02
1172
0.000 5 0.001 3
0.048 6 0.132 5
0.361 8 1.043 8
0.174 6 0.512 7
0.008 9 0.025 7
0.708 0
0.710 1
0.732 8
0.732 0
0.742 7
0.707 89ꢂ3
0.710 46ꢂ2
0.735 63ꢂ3
0.733 40ꢂ2
0.742 74ꢂ2
LMG-11
LMG-20
LMG-21
25.9
17.8
16.3
n
silicified siltstone
siliceous rock
LMG-18 barite-bearing brecciated
ore
6
7
8
LMG-31
LMD-11
LMT-22
massive ore
n
21.8
22.2
8.375
0.429
0.411
21.58
47.45
82.64
0.388 1 1.147 9
0.009 0 0.026 2
0.005 0 0.014 3
0.746 9
0.746 8
0.730 1
0.750 01ꢂ3
0.746 88ꢂ5
0.730 17ꢂ2
altered dolomite
yellowish-brown altered
dolomite
9
LMT-14
white altered dolomite
white altered dolomite
22.2
22.9
17.0
18.9
0.440
0.363
0.165
0.408
94.28
67.55
100.3
108.4
0.004 7 0.013 5
0.005 4 0.015 6
0.001 6 0.004 7
0.003 8 0.010 9
0.730 9
0.741 3
0.718 1
0.715 0
0.730 91ꢂ2
0.741 35ꢂ6
0.718 09ꢂ2
0.714 98ꢂ6
10 LMT-8
11 LMT-12
12 LMD-2
dotted ore
black altered
ferromanganese carbonate
black altered
n
13 LMT-5
3.098
51.87
0.059 7 0.168 9
0.729 9
0.730 34ꢂ3
ferromanganese carbonate
silicified ore
n
n
n
18 LMH-7
20 LMT-15
21 LMB-1
1.746
3.851
6.602
11.95
0.146 1 0.422 7
0.721 4
0.726 7
0.745 7
0.722 53ꢂ1
0.726 94ꢂ4
0.746 88ꢂ1
ore
macrocrystalline altered
dolomite
104.08 0.037 0 0.107 0
43.59
0.151 5 0.439 7
dolomite
dolomite
barite
21.5
21.7
n
DOLSR-1
DOLSR-2
BTSR-1
0.127
0.463
360.6
90.53
70.45
4938
0.0014 0.0041
0.0066 0.0190
0.0730 0.2114
0.7182
0.7398
0.7490
0.71823ꢂ2
0.73989ꢂ2
0.74957ꢂ2
n, not analyzed.
3
Data and discussion
3.1 Rb/Sr ratio
The oxygen isotopic composition is a sensitive indicator of water-rock interactions. The data

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in table 1 show that in the processes of water-rock interaction the Rb/Sr ratios in wall rocks and
ores tend to increase with intensifying water-rock interaction processes. From the wall rocks to the
late-stage ores (relative to the carbonate-type ores) the Rb/Sr ratios have decreased by about two
orders of magnitude, implying the import of Sr into the ore-forming fluids and the leaching-export
of Rb by them. Therefore, in the rocks and ores with extremely low Rb/Sr ratios their Sr isotopic
composition can better reflect the properties and evolution trend of ore-forming fluids.
3.2 Rb-Sr isotopic system
The Sr isotopic composition of wall rocks and ores (table 1 and fig. 1) demonstrates that the
Sr isotopic composition (0.707 98) of the Lower Permian Maokou and Qixia Formation (P1m+q
)
limestones is approximate to that of the contemporaneous seawater (0.707 5)[7]; that of the Middle
Devonian Qujing Formation dolomites (0.710 46) is significantly different from that of the
contemporaneous seawater (0.707 8ü0.708 6), indicating an obvious radiogenic Sr enrichment.
The ores and altered rocks are, to varying degrees, enriched in radiogenic Sr. The Rb/Sr ratio of all
the mineralized samples, except four (0.388 1ü0.146 2), is less than 0.1. So, even if no
correlation is made for radiogenic Sr accumulation in the samples, our conclusions would not be
influenced. Meanwhile, the Sr isotopic composition of these samples with extremely low Rb/Sr
ratios can be regarded as the initial Sr composition of ore-forming hydrothermal solutions during
metallogenesis. The 87Sr/86Sr ratios in the clastic rock-type ores range from 0.722 531 to 0.750 01
while those of the carbonate-type ores, from 0.714 98 to 0.746 88, indicating that the ore-forming
fluids once flew through the rocks or strata enriched in radiogenic Sr, or at least the Sr was
derived from a source region with a high Sr isotopic ratio. A source region extremely high in
87Sr/86Sr ratio must possess or must have once possessed a high Rb/Sr ratio, hence yielding
relatively old ages. Regionally, the most possible 87Sr/86Sr-high source region is the pre-Cambrian
basement composed mainly of metamorphic rocks. According to Chen et al.[8], the initial 87Sr/86Sr
ratio in quartz fluid inclusions from the Lalachang Cu deposits hosted in the Proterozoic Hekou
87
Group is 0.727 5 (995 Ma in age). As reported by Li et al.[9], the initial Sr/86Sr isotopic ratio in
the Yingming Formation dolomites at Dongchuan is 0.728 8 (984 Ma in age), that of the Chahe
Formation carbonaceous slates of the Hekou Group 0.728 3 (1 006 Ma in age), and that of the
Yingming Formation slates at Tongchang, Yimen, 0.724 9 (1 115 Ma in age). All this goes to show
that the Proterozoic basement strata (the Kunyang and Hekou groups) can be regarded as the
source region of highly radiogenic Sr in the ore-forming fluids. Especially when the basement
rocks were leached by ore-forming fluids, which led to the preferential decomposition of minerals
enriched in highly radiogenic Sr, Sr isotopic dynamic non-equilibrium fractionation effect
between source rocks and fluids would take place. As a result, the fluids would possess a higher Sr
isotopic ratio than the rocks in the water-rock reaction system. The 87Sr/86Sr ratios in the Emeishan
basalt are within the range of 0.705 5ü0.708 2[10], with an initial Sr ratio being 0.704 41ü
0.706 83[11]. From the above discussion it can be seen clearly that the Emeishan basalt could by no

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341
Fig. 1. The Sr isotopic composition of rocks and ores in the Lemachang independent Ag deposit, northeastern
Yunnan. Ĵ, Modern seawater; ƶ, altered dolomite; ͪ, dolomite; Ƶ, carbonate-type ore;
silicified rock; Ʒ, clastic rock-type ore; ƿ, unaltered carbonate rock.
, barite; Ƹ,
means be regarded as the source region of highly radiogenic Sr in the ore-forming fluids.
3.3 Sr-87Sr/86Sr system
The Sr contents and Sr isotopic compositions of rocks and ores in the Lemachang inde-
pendent Ag deposit (table 1, fig. 2)
indicate that Sr and Sr isotopic
exchange did occur between the
ore-forming fluids and the wall
rocks (dolomite). Although the
mechanism of fluid mixing is
highly possible, clearly it cannot
be interpreted in terms of a simple
binary mixing model (fig. 2). The
C and O isotopic analyses of hydr-
Fig. 2. 87Sr/86Sr-Sr plot of the Lemachang independent Ag deposit in
othermal and altered dolomites
northeastern Yunnan. 嗟, Carbonate-type ore; Ƶ, ore-forming fluid; ƶ,
massive Ag ore; Ʒ, clastic rock-type ore; ƿ, unaltered carbonate rock.
and REE and Sm-Nd isotopic
studies all strongly support the mechanism of intensive water-rock interaction1).
In order to carefully investigate the Sr-87Sr/86Sr system in rocks and ores of the Lemachang
independent Ag deposit, we have adopted the model which is used to describe Sr and Sr
1) See footnote 3) on page 338.

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isotopic exchange in hydrothermal altera-
tion processes at mid-ocean ridges[13, 14]
.
As this model is based on the water-rock
interaction system, aiming at studying the
Sr and Sr isotopic exchange between fluids
and rocks, it is suitable for the study of
wall-rock alteration processes essentially
involving water-rock interactions in hydr-
othermal deposits though the partitioning
coefficient between fluid and dolomite[15, 16]
and barite[17] should be taken as the
partitioning coefficient of Sr in the model
so as to make the model well coordinate
with alterations such as dolomitization and
silicification- baritization in the Lemachang
independent Ag deposit. As revealed by the
model, the mechanism of water-rock
interaction involved in the formation of
the carbonate-type ores is intermediate
between first dissolution-second precipita-
tion (fig. 3(b), fig. 4(b)) and contempor-
aneous precipitation-dissolution (fig. 3(c),
fig. 4(b)) (paths El and E2), or between
first precipitation-second dissolution (fig.
3(a), fig. 4(b)) and contemporaneous
Fig. 3. The evolution diagram of the Sr-87Sr/86Sr system in ores
from the Lemachang independent Ag deposit. Fluid evolution model
after Berndt et al.[12]. Dolomite: Sr=100 ꢅg/g , 87Sr/86Sr=0.710 46;
fluid(1):Sr=47 ꢅg/g; 87Sr/86Sr=0.750 0; fluid (2): Sr=3 ꢅg/g,
87Sr/86Sr=0.750 0. 嗟, Carbonate rock-type ore; Ƶ, ore-forming fluid;
ƶ, massive Ag ore; Ƹ, clastic rock-type ore. (a) Closed system (the
first-dissolution model); (b) open system I (the first-precipitation precipitation-dissolution (paths D1 and
model); (c) open system II (the contemporaneous-dissolution-
precipitation model).
D2). The modelling results also show that
the concentrations of Sr in the ore-forming
fluids are 3×10-6, i.e. ore-forming fluid (2) is more coincident with the geological fact. It is
obtained from this that the fluid/rock ratios are within the range of about 5ü50. The water-rock
interaction path for the formation of silicified-baritized clastic rock-type ores can be described as
first dissolution-second precipitation, or contemporaneous precipitation-dissolution. The
fluid/rock ratio varies over a large range. Strongly baritized ores seem to have been deposited and
crystallized directly from ore-forming solutions with the concentrations of Sr in the ore-forming
fluids amounting up to 47 h10-6 and the fluid/rock ratio being high in the process of
mineralization (>100). Fig. 4(a) presents a possible evolution path for the ore-forming fluids. The
evolution path of fluids responsible for the carbonate rock-type ores is marked by D2 or E2 which
lies between the path of first dissolution-second precipitation and that of contemporaneous

No. 4
Sr ISOTOPE GEOCHEMISTRY OF LEMACHANG Ag ORE DEPOSIT
343
precipitation-dissolution; that of fluids
forming the clastic rock-type ores is
described
as
contemporaneous
precipitation-second dissolution or first
dissolution-second precipitation; and
that of fluids producing the strongly
baritized
ores
is
depicted
as
precipitation-crystallization. Of course,
the authors noticed the possibility of
mutual conversion between fluid (1)
and fluid (2). That is to say, when fluid
(1) undergoes the precipitation-
crystallization of Sr-bearing phase, it
can be converted to fluid (2); when the
gas phase in fluid (2) is released in large
amounts, it can be converted to fluid (1).
Based on the evidence that no boiled
immiscible fluid inclusions have been
found in barite veins both in the field
and under the microscope1), it is
deduced that during the initial evolution
stage the ore-forming fluids containing
as much as 47 ꢅg/g Sr would evolve
into the fluids with 3 ꢅg/g Sr after barite
was precipitated. The subsequent
evolution stages are the same as what is
described previously. The fluids reacted
Fig. 4. The evolution diagram of the Sr-87Sr/86Sr system in the
Lemachang independent Ag deposit, northeastern Yunnan. 嗟 ,
Carbonate rock-type ore; Ƶ, ore-forming fluid; ƶ, massive Ag ore;
Ƹ, clastic rock-type ore. (a) Evolution diagram of ore-forming fluids.
A1 and A2 represent the evolution path of first dissolution-second
precipitation; B1 and B2 stand for the evolution path of first
precipitation-second dissolution; C indicates the evolution path of
contemporaneous dissolution-precipitation. The evolution path of fluids
recommended by D and E. The evolution model after Berndt et al.[13]. (b)
The evolution diagram of altered rocks. A1 and A2 represent the
evolution path of first dissolution-second precipitation; B1 and B2 stand
for the evolution path of first precipitation-second dissolution; C, the
evolution path of contemporaneous dissolution-precipitation; D and E,
the recommended evolution path. The evolution model after Ridley et
al.[14]
.
with the wall rocks on a large scale, followed by ore deposition.
3.4 ꢀ18O-Sr isotopic system
The evolution model of O and Sr isotopes in rocks and ores from the Lemachang
independent deposit (fig. 5) suggests that when large-scaled water-rock interactions occurred, the
Sr concentrations of the ore-forming fluids would be 3 ꢅg/g, with the Sr and O isotopic
compositions being 0.750 and 7.0‰, respectively. Such ore-forming fluids could not be either
derived from cognate seawater or from metamorphic water, not to say from non-evolved meteoric
water. They are highly possible to have been derived from deeply circulated and evolved meteoric
1) See footnote 3) on page 338.

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Vol. 43
Fig. 5. ꢀ18O-87Sr/86Sr evolution diagram of the Lemachang independent Ag deposit, northeastern Yunnan. Sr, O
isotope water-rock exchange interaction equations after Taylor et al.[18,19] and McCulloch et al.[20,21]
metamorphic water after Sheppard[22] and Muller et al.[3]; cognate seawater after Sheppard[22] and Burke et al.[23]
;
;
meteoric water after Wang[24] and Wang[24] and Faure[2]; dolomite-water oxygen isotope fractionation equation
after Land[25]. ꢀ, Carbonate rock-type ore; ƾ, ore-forming fluid; Ƶ, unaltered rock; Ʒ, clastic rock-type ore.
Meteoric water: Sr=0.4 ꢅg/g, 87Sr/86=0.709 2, ꢀ18O=ꢁ10.5‰; cognate seawater: Sr=8.0 ꢅg/g, 87Sr/86=0.710 0,
ꢀ18O=0.0‰; clastic rocks: Sr=20 ꢅg/g, 87Sr/86=0.720, ꢀ18O=19.0‰; metamorphic water : Sr=0.4 ꢅg/g,
87Sr/86=0.714 3, ꢀ18O=15‰; ore-forming fluid: Sr=3.0 ꢅg/g, 87Sr/86=0.750, ꢀ18O=7.0‰; carbonates: Sr=142.0
ꢅg/g, 87Sr/86=0.709, ꢀ18O=27.0‰ .
water or formation water. In regard to the carbonate rock-type ores the ore-forming temperatures
range from 150 to 250ć, 200ü260ć for the clastic rock-type ores. On the assumption that the
Sr concentrations of ore-forming fluids are 47 ꢅg/g, it is indicated that the modeling result cannot
be well fitted with geological facts. This is generally in consistence with the above analysis of the
Sr-87Sr/86Sr system.
3.5 Water-rock interaction and the independent Ag deposit
The Lemachang independent Ag deposit must have at least experienced water-rock
interaction twice. First, meteoric water or formation water found its way into the ore-forming
material source region and under the conditions of low water-rock ratio and at about 300ć the
water reacted with the source rocks to extract ore-forming elements (Ag, Cu, Pb, Zn, As, Sb, S,
etc.) . As a result, the meteoric or formation water was transformed into ore-forming fluid1). The
low water/rock ratio and water-rock interaction at about 300 ć are favorable to the
beyond-the-limit separation of Ag from base metals[26,27]. When the fluids moved to the locus of
1) See footnote 3) on page 338.

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Sr ISOTOPE GEOCHEMISTRY OF LEMACHANG Ag ORE DEPOSIT
345
ore deposition, they would react with the wall rocks of different lithological characters, hence
leading to different types of alteration and different types of mineralization. Low ore-forming
temperature (150ü250ć) and enrichment of ore-forming fluids in As and Sb are favorable to the
preferential combination of Ag with As and Sb to form independent sulfosalts of Ag, followed by
further separation of Ag from Pb and Zn to become more concentrated. Therefore, water-rock
interaction is the major mechanism of continuous enrichment of Ag and is also the key to the
formation of independent Ag deposits.
4
Conclusions
Sr isotopic geochemical studies and theoretical modeling on a systematic basis of wall rocks
and ores from the Lemachang independent Ag deposit in northeastern Yunnan lead us to draw the
following conclusions:
1) It is evidenced that the ore-forming fluids had flown through radiogenic Sr-enriched rocks
or strata before they found their way into the locus of ore deposition, and this radiogenic
Sr-enriched source region seems to be the Proterozoic basement (the Kunyang and Hekou groups)
and at the same time it would be the source region of Ag.
2) Water-rock interaction is the main mechanism of Ag ore deposition with water/rock ratio
being as large as about 5ü50.
3) The initial concentrations of the ore-forming fluids are 3 ꢅg/g with the Sr, O isotopic
compositions being 0.750 and 7‰, respectively. The ore-forming temperatures are 150ü250ć
for the carbonate rock-type ores and 200ü260ć for the clastic rock-type ores. Evidence shows
that the ore-forming fluids seem to have been derived from deeply circulated and evolved
meteoric water or formation water.
Acknowledgements Sr isotopic analysis was accomplished at the Laboratory of Radioactive Isotopes for Youth,
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences and the Laboratory of Isotopes, Institute of Geology,
Chinese Academy of Sciences. Oxygen isotopic analysis was conducted at the Laboratory of Stable Isotopes, Institute of Mineral
Deposits, Chinese Academy of Geological Sciences; bulk chemical analysis of rocks and ores was carried out at the Institute of
Geochemistry, Chinese Academy of Sciences; great help with field work was offered by Chief Engineer Zhang Yifei in the
Yunnan Provincial Bureau of Geology and Mineral Resources and by the No.1 Branch of the No.1 Geological Party. Here the
authors wish to thank them all. This research project was supported jointly by the Project A-30- 5 and the Preselected Project
95-Yu-25 under the State Climbing Program.
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