[lcy2]

will they react?   cos' i put in a considerable amount of each, and all i've got is white cloud that should be CaCO3 and nothing more.  Phenol shows.  There is free flowing Cl^- in solution, but i'm not sure whether it reacts to completion.  CO₂ is released after HCl has contact with the insoluble part.

Can someone please help me?

[Borek]

There is no easy answer... You will have to check out cemplexation constants for CaClx, ZnClx, Ca(CO3)x, Zn(CO3)x and solubility proucts for ZnCO3 and CaCO3. Not to mention CO3(2-) hydrolysis and OH- complexes...

Basically ZnCO3 is about 100 times less soluble then CaCO3 so you may expect something like

ZnCl2(aq) + CaCO3(s) -> ZnCO3(s) + CaCl2

but it will be very slow and difficult to spot, as the solution will look all the same, with white precipitate.

[lcy2]

interesting.  What i've found later in some books was...
the product: ZnCO3*2Zn(OH)2 + CO2 + 3CaCl2

the reactant has to also include H2O