Table 1. Lead isotope compositions.

		Spring	Summer	Autumn	Winter
208Pb/204Pb	Mean	36.773	37.033	36.795	36.596
	Range	36.710–36.888	36.471–37.949	36.145–37.559	36.233–37.166
208Pb/206Pb	Mean	2.184	2.162	2.171	2.189
	Range	2.165–2.204	2.094–2.197	2.112–2.206	2.160–2.202
207Pb/204Pb	Mean	15.568	15.600	15.529	15.517
	Range	15.443–15.688	15.429–15.761	15.129–15.732	15.350–15.773
206Pb/204Pb	Mean	16.838	17.134	16.957	16.720
	Range	16.678–16.971	16.758–18.121	16.490–17.787	16.505–17.034
206Pb/207Pb	Mean	1.082	1.098	1.092	1.078
	Range	1.063–1.098	1.069–1.168	1.061–1.132	1.069–1.100