I have more than 500 ores in my game. How to handle them?

Well if you want to find all the ores in one place, you could use :GetDescentdants()

If you group all the ores into a single model or folder it would go like:

game.Workspace.OresInAModelInThis:GetDescendants(Ores)

So, you have a list of everything in "OresInThisModel" and everything inside the all children of that.

For more info on :GetDescendants() look on the RobloxWiki

From there you can do two things.

One

If you go ahead with a script in each ore, you can use the GetDescandants and do this:

game.Workspace.OresInAModelInThis:GetDescendants(Ores)

if Ores:IsA("Script") == true then 
Ores.Disabled = false 

--Rest of script here

Two

You could control everything from the descendant.

game.Workspace.OresInAModelInThis:GetDescendants(Ores)

if Ores:IsA("Part") == true then --Or whatever instance the ores is 

--Rest of script here because I don't know your workspace

--Include a local for the Health value, find it using If value IsA('IntValue')
--If it goes down to zero 'if health.value == 0 then'
--Then local health.Parent:Destroy()

For more info on IsA you can check that on the wiki too.